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Overview

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Hunter is a flexible code tracing toolkit, not for measuring coverage, but for debugging, logging, inspection and other nefarious purposes. It has a simple Python API, a convenient terminal API and a CLI tool to attach to processes.

• Free software: BSD 2-Clause License

Installation

pip install hunter

Documentation

https://python-hunter.readthedocs.io/

Getting started

Basic use involves passing various filters to the trace option. An example:

import hunter
hunter.trace(module='posixpath', action=hunter.CallPrinter)

import os
os.path.join('a', 'b')

That would result in:

>>> os.path.join('a', 'b')
         /usr/lib/python3.6/posixpath.py:75    call      => join(a='a')
         /usr/lib/python3.6/posixpath.py:80    line         a = os.fspath(a)
         /usr/lib/python3.6/posixpath.py:81    line         sep = _get_sep(a)
         /usr/lib/python3.6/posixpath.py:41    call         => _get_sep(path='a')
         /usr/lib/python3.6/posixpath.py:42    line            if isinstance(path, bytes):
         /usr/lib/python3.6/posixpath.py:45    line            return '/'
         /usr/lib/python3.6/posixpath.py:45    return       <= _get_sep: '/'
         /usr/lib/python3.6/posixpath.py:82    line         path = a
         /usr/lib/python3.6/posixpath.py:83    line         try:
         /usr/lib/python3.6/posixpath.py:84    line         if not p:
         /usr/lib/python3.6/posixpath.py:86    line         for b in map(os.fspath, p):
         /usr/lib/python3.6/posixpath.py:87    line         if b.startswith(sep):
         /usr/lib/python3.6/posixpath.py:89    line         elif not path or path.endswith(sep):
         /usr/lib/python3.6/posixpath.py:92    line         path += sep + b
         /usr/lib/python3.6/posixpath.py:86    line         for b in map(os.fspath, p):
         /usr/lib/python3.6/posixpath.py:96    line         return path
         /usr/lib/python3.6/posixpath.py:96    return    <= join: 'a/b'
'a/b'

In a terminal it would look like:

Another useful scenario is to ignore all standard modules and force colors to make them stay even if the output is redirected to a file.

import hunter
hunter.trace(stdlib=False, action=hunter.CallPrinter(force_colors=True))

Actions

Output format can be controlled with “actions”. There’s an alternative CodePrinter action that doesn’t handle nesting (it was the default action until Hunter 2.0).

If filters match then action will be run. Example:

import hunter
hunter.trace(module='posixpath', action=hunter.CodePrinter)

import os
os.path.join('a', 'b')

That would result in:

>>> os.path.join('a', 'b')
         /usr/lib/python3.6/posixpath.py:75    call      def join(a, *p):
         /usr/lib/python3.6/posixpath.py:80    line          a = os.fspath(a)
         /usr/lib/python3.6/posixpath.py:81    line          sep = _get_sep(a)
         /usr/lib/python3.6/posixpath.py:41    call      def _get_sep(path):
         /usr/lib/python3.6/posixpath.py:42    line          if isinstance(path, bytes):
         /usr/lib/python3.6/posixpath.py:45    line              return '/'
         /usr/lib/python3.6/posixpath.py:45    return            return '/'
                                               ...       return value: '/'
         /usr/lib/python3.6/posixpath.py:82    line          path = a
         /usr/lib/python3.6/posixpath.py:83    line          try:
         /usr/lib/python3.6/posixpath.py:84    line              if not p:
         /usr/lib/python3.6/posixpath.py:86    line              for b in map(os.fspath, p):
         /usr/lib/python3.6/posixpath.py:87    line                  if b.startswith(sep):
         /usr/lib/python3.6/posixpath.py:89    line                  elif not path or path.endswith(sep):
         /usr/lib/python3.6/posixpath.py:92    line                      path += sep + b
         /usr/lib/python3.6/posixpath.py:86    line              for b in map(os.fspath, p):
         /usr/lib/python3.6/posixpath.py:96    line          return path
         /usr/lib/python3.6/posixpath.py:96    return        return path
                                               ...       return value: 'a/b'
'a/b'

• or in a terminal:

---

Another useful action is the VarsPrinter:

import hunter
# note that this kind of invocation will also use the default `CallPrinter` action
hunter.trace(hunter.Q(module='posixpath', action=hunter.VarsPrinter('path')))

import os
os.path.join('a', 'b')

That would result in:

>>> os.path.join('a', 'b')
     /usr/lib/python3.6/posixpath.py:75    call      => join(a='a')
     /usr/lib/python3.6/posixpath.py:80    line         a = os.fspath(a)
     /usr/lib/python3.6/posixpath.py:81    line         sep = _get_sep(a)
     /usr/lib/python3.6/posixpath.py:41    call      [path => 'a']
     /usr/lib/python3.6/posixpath.py:41    call         => _get_sep(path='a')
     /usr/lib/python3.6/posixpath.py:42    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:42    line            if isinstance(path, bytes):
     /usr/lib/python3.6/posixpath.py:45    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:45    line            return '/'
     /usr/lib/python3.6/posixpath.py:45    return    [path => 'a']
     /usr/lib/python3.6/posixpath.py:45    return       <= _get_sep: '/'
     /usr/lib/python3.6/posixpath.py:82    line         path = a
     /usr/lib/python3.6/posixpath.py:83    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:83    line         try:
     /usr/lib/python3.6/posixpath.py:84    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:84    line         if not p:
     /usr/lib/python3.6/posixpath.py:86    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:86    line         for b in map(os.fspath, p):
     /usr/lib/python3.6/posixpath.py:87    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:87    line         if b.startswith(sep):
     /usr/lib/python3.6/posixpath.py:89    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:89    line         elif not path or path.endswith(sep):
     /usr/lib/python3.6/posixpath.py:92    line      [path => 'a']
     /usr/lib/python3.6/posixpath.py:92    line         path += sep + b
     /usr/lib/python3.6/posixpath.py:86    line      [path => 'a/b']
     /usr/lib/python3.6/posixpath.py:86    line         for b in map(os.fspath, p):
     /usr/lib/python3.6/posixpath.py:96    line      [path => 'a/b']
     /usr/lib/python3.6/posixpath.py:96    line         return path
     /usr/lib/python3.6/posixpath.py:96    return    [path => 'a/b']
     /usr/lib/python3.6/posixpath.py:96    return    <= join: 'a/b'
'a/b'

In a terminal it would look like:

---

You can give it a tree-like configuration where you can optionally configure specific actions for parts of the tree (like dumping variables or a pdb set_trace):

from hunter import trace, Q, Debugger
from pdb import Pdb

trace(
    # drop into a Pdb session if ``foo.bar()`` is called
    Q(module="foo", function="bar", kind="call", action=Debugger(klass=Pdb))
    |  # or
    Q(
        # show code that contains "mumbo.jumbo" on the current line
        lambda event: event.locals.get("mumbo") == "jumbo",
        # and it's not in Python's stdlib
        stdlib=False,
        # and it contains "mumbo" on the current line
        source__contains="mumbo"
    )
)

import foo
foo.func()

With a foo.py like this:

def bar():
    execution_will_get_stopped  # cause we get a Pdb session here

def func():
    mumbo = 1
    mumbo = "jumbo"
    print("not shown in trace")
    print(mumbo)
    mumbo = 2
    print(mumbo) # not shown in trace
    bar()

We get:

>>> foo.func()
not shown in trace
    /home/ionel/osp/python-hunter/foo.py:8     line          print(mumbo)
jumbo
    /home/ionel/osp/python-hunter/foo.py:9     line          mumbo = 2
2
    /home/ionel/osp/python-hunter/foo.py:1     call      def bar():
> /home/ionel/osp/python-hunter/foo.py(2)bar()
-> execution_will_get_stopped  # cause we get a Pdb session here
(Pdb)

In a terminal it would look like:

Tracing processes

In similar fashion to strace Hunter can trace other processes, eg:

hunter-trace --gdb -p 123

If you wanna play it safe (no messy GDB) then add this in your code:

from hunter import remote
remote.install()

Then you can do:

hunter-trace -p 123

See docs on the remote feature.

Note: Windows ain’t supported.

Environment variable activation

For your convenience environment variable activation is available. Just run your app like this:

PYTHONHUNTER="module='os.path'" python yourapp.py

On Windows you’d do something like:

set PYTHONHUNTER=module='os.path'
python yourapp.py

The activation works with a clever .pth file that checks for that env var presence and before your app runs does something like this:

from hunter import *
trace(<whatever-you-had-in-the-PYTHONHUNTER-env-var>)

Note that Hunter is activated even if the env var is empty, eg: PYTHONHUNTER="".

Environment variable configuration

Sometimes you always use the same options (like stdlib=False or force_colors=True). To save typing you can set something like this in your environment:

PYTHONHUNTERCONFIG="stdlib=False,force_colors=True"

This is the same as PYTHONHUNTER="stdlib=False,action=CallPrinter(force_colors=True)".

Notes:

• Setting PYTHONHUNTERCONFIG alone doesn’t activate hunter.

• All the options for the builtin actions are supported.

• Although using predicates is supported it can be problematic. Example of setup that won’t trace anything:

  PYTHONHUNTERCONFIG="Q(module_startswith='django')"
  PYTHONHUNTER="Q(module_startswith='celery')"
  

  which is the equivalent of:

  PYTHONHUNTER="Q(module_startswith='django'),Q(module_startswith='celery')"
  

  which is the equivalent of:

  PYTHONHUNTER="Q(module_startswith='django')&Q(module_startswith='celery')"
  

Filtering DSL

Hunter supports a flexible query DSL, see the introduction.

Development

To run the all tests run:

tox

Design notes

Hunter doesn’t do everything. As a design goal of this library some things are made intentionally austere and verbose (to avoid complexity, confusion and inconsistency). This has few consequences:

• There are Operators but there’s no negation operator. Instead you’re expected to negate a Query object, eg: ~Q(module='re').
• There are no specialized operators or filters - all filters behave exactly the same. For example:
  • No filter for packages. You’re expected to filter by module with an operator.
  • No filter for arguments, return values or variables. You’re expected to write your own filter function and deal with the problems of poking into objects.
• Layering is minimal. There’s are some helpers that do some argument processing and conversions to save you some typing but that’s about it.
• The library doesn’t try to hide the mechanics of tracing in Python - it’s 1:1 regarding what Python sends to a trace function if you’d be using sys.settrace.
• Doesn’t have any storage. You are expected to redirect output to a file.

You should look at it like it’s a tool to help you understand and debug big applications, or a framework ridding you of the boring parts of settrace, not something that helps you learn Python.

FAQ

Why not Smiley?

There’s some obvious overlap with smiley but there are few fundamental differences:

• Complexity. Smiley is simply over-engineered:

  • It uses IPC and a SQL database.
  • It has a webserver. Lots of dependencies.
  • It uses threads. Side-effects and subtle bugs are introduced in your code.
  • It records everything. Tries to dump any variable. Often fails and stops working.

  Why do you need all that just to debug some stuff in a terminal? Simply put, it’s a nice idea but the design choices work against you when you’re already neck-deep into debugging your own code. In my experience Smiley has been very buggy and unreliable. Your mileage may vary of course.

• Tracing long running code. This will make Smiley record lots of data, making it unusable.

  Now because Smiley records everything, you’d think it’s better suited for short programs. But alas, if your program runs quickly then it’s pointless to record the execution. You can just run it again.

  It seems there’s only one situation where it’s reasonable to use Smiley: tracing io-bound apps remotely. Those apps don’t execute lots of code, they just wait on network so Smiley’s storage won’t blow out of proportion and tracing overhead might be acceptable.

• Use-cases. It seems to me Smiley’s purpose is not really debugging code, but more of a “non interactive monitoring” tool.

In contrast, Hunter is very simple:

• Few dependencies.

• Low overhead (tracing/filtering code has an optional Cython extension).

• No storage. This simplifies lots of things.

  The only cost is that you might need to run the code multiple times to get the filtering/actions right. This means Hunter is not really suited for “post-mortem” debugging. If you can’t reproduce the problem anymore then Hunter won’t be of much help.

Why not pytrace?

Pytrace is another tracer tool. It seems quite similar to Smiley - it uses a sqlite database for the events, threads and IPC, thus it’s reasonable to expect the same kind of problems.

Why not PySnooper or snoop?

snoop is a refined version of PySnooper. Both are more suited to tracing small programs or functions as the output is more verbose and less suited to the needs of tracing a big application where Hunter provides more flexible setup, filtering capabilities, speed and brevity.

Why not coverage?

For purposes of debugging coverage is a great tool but only as far as “debugging by looking at what code is (not) run”. Checking branch coverage is good but it will only get you as far.

From the other perspective, you’d be wondering if you could use Hunter to measure coverage-like things. You could do it but for that purpose Hunter is very “rough”: it has no builtin storage. You’d have to implement your own storage. You can do it but it wouldn’t give you any advantage over making your own tracer if you don’t need to “pre-filter” whatever you’re recording.

In other words, filtering events is the main selling point of Hunter - it’s fast (cython implementation) and the query API is flexible enough.

Projects using Hunter

Noteworthy usages or Hunter (submit a PR with your project if you built a tool that relies on hunter):

• Crunch-io/diagnose - a runtime instrumentation library.
• talwrii/huntrace - an alternative cli (similar to ltrace).
• anki-code/xunter - a profiling tool made specifically for the xonsh shell.

More projects using it at https://github.com/ionelmc/python-hunter/network/dependents

Installation

At the command line:

pip install hunter

Introduction

Installation

To install hunter run:

pip install hunter

The trace function

The hunter.trace function can take 2 types of arguments:

• Keyword arguments like module, function or action (see hunter.Event for all the possible filters).
• Callbacks that take an event argument:
  • Builtin predicates like: hunter.predicates.Query, hunter.When, hunter.And or hunter.Or.
  • Actions like: hunter.actions.CodePrinter, hunter.actions.Debugger or hunter.actions.VarsPrinter
  • Any function. Or a disgusting lambda.

Note that hunter.trace will use hunter.Q when you pass multiple positional arguments or keyword arguments.

The Q function

The hunter.Q() function provides a convenience API for you:

• Q(module='foobar') is converted to Query(module='foobar').
• Q(module='foobar', action=Debugger) is converted to When(Query(module='foobar'), Debugger).
• Q(module='foobar', actions=[CodePrinter, VarsPrinter('name')]) is converted to When(Query(module='foobar'), CodePrinter, VarsPrinter('name')).
• Q(Q(module='foo'), Q(module='bar')) is converted to And(Q(module='foo'), Q(module='bar')).
• Q(your_own_callback, module='foo') is converted to And(your_own_callback, Q(module='foo')).

Note that the default junction hunter.Q() uses is hunter.predicates.And.

Composing

All the builtin predicates (hunter.predicates.Query, hunter.predicates.When, hunter.predicates.And, hunter.predicates.Not and hunter.predicates.Or) support the |, & and ~ operators:

• Query(module='foo') | Query(module='bar') is converted to Or(Query(module='foo'), Query(module='bar'))
• Query(module='foo') & Query(module='bar') is converted to And(Query(module='foo'), Query(module='bar'))
• ~Query(module='foo') is converted to Not(Query(module='foo'))

Operators

New in version 1.0.0: You can add startswith, endswith, in, contains, regex, lt, lte, gt, gte to your keyword arguments, just like in Django. Double underscores are not necessary, but in case you got twitchy fingers it’ll just work - filename__startswith is the same as filename_startswith.

New in version 2.0.0: You can also use these convenience aliases: sw (startswith), ew (endswith), rx (regex) and has (contains).

Examples:

• Query(module_in=['re', 'sre', 'sre_parse']) will match events from any of those modules.
• ~Query(module_in=['re', 'sre', 'sre_parse']) will match events from any modules except those.
• Query(module_startswith=['re', 'sre', 'sre_parse']) will match any events from modules that starts with either of those. That means repr will match!
• Query(module_regex='(re|sre.*)$') will match any events from re or anything that starts with sre.

Note

If you want to filter out stdlib stuff you’re better off with using Query(stdlib=False).

Activation

You can activate Hunter in three ways.

from code

import hunter
hunter.trace(
    ...
)

with an environment variable

Set the PYTHONHUNTER environment variable. Eg:

PYTHONHUNTER="module='os.path'" python yourapp.py

On Windows you’d do something like:

set PYTHONHUNTER=module='os.path'
python yourapp.py

The activation works with a clever .pth file that checks for that env var presence and before your app runs does something like this:

from hunter import *
trace(
    <whatever-you-had-in-the-PYTHONHUNTER-env-var>
)

That also means that it will do activation even if the env var is empty, eg: PYTHONHUNTER="".

with a CLI tool

If you got an already running process you can attach to it with hunter-trace. See Remote tracing for details.

Remote tracing

Hunter supports tracing local processes, with two backends: manhole and GDB. For now Windows isn’t supported.

Using GDB is risky (if anything goes wrong your process will probably be hosed up badly) so the Manhole backend is recommended. To use it:

from hunter import remote
remote.install()

You should put this somewhere where it’s run early in your project (settings or package’s __init__.py file).

The remote.install() takes same arguments as manhole.install(). You’ll probably only want to use verbose=False …

The CLI

usage: hunter-trace [-h] -p PID [-t TIMEOUT] [--gdb] [-s SIGNAL]
                [OPTIONS [OPTIONS ...]]

positional arguments:

OPTIONS

optional arguments:

-h, --help	show this help message and exit
-p PID, --pid PID
	A numerical process id.
-t TIMEOUT, --timeout TIMEOUT
	Timeout to use. Default: 1 seconds.
--gdb	Use GDB to activate tracing. WARNING: it may deadlock the process!
-s SIGNAL, --signal SIGNAL
	Send the given SIGNAL to the process before connecting.

The OPTIONS are hunter.trace() arguments.

Configuration

Default predicates and action kwargs defaults can be configured via a PYTHONHUNTERCONFIG environment variable.

All the actions kwargs:

• klass
• stream
• force_colors
• force_pid
• filename_alignment
• thread_alignment
• pid_alignment
• repr_limit
• repr_func

Example:

PYTHONHUNTERCONFIG="stdlib=False,force_colors=True"

This is the same as PYTHONHUNTER="stdlib=False,action=CallPrinter(force_colors=True)".

Notes:

• Setting PYTHONHUNTERCONFIG alone doesn’t activate hunter.

• All the options for the builtin actions are supported.

• Although using predicates is supported it can be problematic. Example of setup that won’t trace anything:

  PYTHONHUNTERCONFIG="Q(module_startswith='django')"
  PYTHONHUNTER="Q(module_startswith='celery')"
  

  which is the equivalent of:

  PYTHONHUNTER="Q(module_startswith='django'),Q(module_startswith='celery')"
  

  which is the equivalent of:

  PYTHONHUNTER="Q(module_startswith='django')&Q(module_startswith='celery')"
  

Filtering

A list of all the keyword filters that hunter.trace or hunter.Q accept:

• arg - you probably don’t care about this - it may have a value for return/exception events
• builtin (bool) - True if function is a builtin function
• calls (int) - a call counter, you can use it to limit output by using a lt operator
• depth (int) - call depth, starts from 0, increases for call events and decreases for returns
• filename (str)
• fullsource (str) - sourcecode for the executed lines (may be multiple lines in some situations)
• function (str) - function name
• globals (dict) - global variables
• instruction (int or str, depending on Python version) - current executed bytecode, see Silenced exception runtime analysis for example usage
• kind (str) - one of ‘call’, ‘exception’, ‘line’ or ‘return’
• lineno (int)
• locals (dict) - local variables
• module (str) - dotted module
• source (str) - sourcecode for the executed line
• stdlib (bool) - True if module is from stdlib
• threadid (int)
• threadname (str) - whatever threading.Thread.name returns

You can append operators to the above filters. Note that some of of the filters won’t work well with the bool or int types.

• contains - works best with str, for example module_contains='foobar' translates to 'foobar' in event.module
• has - alias for contains
• endswith - works best with str, for example module_endswith='foobar' translates to event.module.endswith('foobar'). You can also pass in a iterable, example module_endswith=('foo', 'bar') is acceptable
• ew - alias for endswith
• gt - works best with int, for example lineno_gt=100 translates to event.lineno > 100
• gte - works best with int, for example lineno_gte=100 translates to event.lineno >= 100
• in - a membership test, for example module_in=('foo', 'bar') translates to event.module in ('foo', 'bar'). You can use any iterable, for example module_in='foo bar' translates to event.module in 'foo bar', and that would probably have the same result as the first example
• lt - works best with int, for example calls_lt=100 translates to event.calls < 100
• lte - works best with int, for example depth_lte=100 translates to event.depth <= 100
• regex - works best with str, for example module_regex=r'(test|test.*)\b' translates to re.match(r'(test|test.*)\b', event.module)
• rx - alias for regex
• startswith - works best with str, for example module_startswith='foobar' translates to event.module.startswith('foobar'). You can also pass in a iterable, example module_startswith=('foo', 'bar') is acceptable
• sw - alias for startswith

Notes:

• you can also use double underscore (if you’re too used to Django query lookups), eg: module__has='foobar' is acceptable
• there’s nothing smart going on for the dots in module names so sometimes you might need to account for said dots:
  • module_sw='foo' will match "foo.bar" and "foobar" - if you want to avoid matchin the later you could do either of:
    • Q(module='foo')|Q(module_sw='foo.')
    • Q(module_rx=r'foo($|\.)') - but this might cost you in speed
    • Q(filename_sw='/path/to/foo/') - probably the fastest
    • Q(filename_has='/foo/') - avoids putting in the full path but might match unwanted paths

Cookbook

When in doubt, use Hunter.

Walkthrough

Sometimes you just want to get an overview of an unfamiliar application code, eg: only see calls/returns/exceptions.

In this situation, you could use something like ~Q(kind="line"),~Q(module_in=["six","pkg_resources"]),~Q(filename=""),stdlib=False. Lets break that down:

• ~Q(kind="line") means skip line events (~ is a negation of the filter).
• stdlib=False means we don’t want to see anything from stdlib.
• ~Q(module_in=["six","pkg_resources")] means we’re tired of seeing stuff from those modules in site-packages.
• ~Q(filename="") is necessary for filtering out events that come from code without a source (like the interpreter bootstrap stuff).

You would run the application (in Bash) like:

PYTHONHUNTER='~Q(kind="line"),~Q(module_in=["six","pkg_resources"]),~Q(filename=""),stdlib=False' myapp (or python myapp.py)

Additionally you can also add a depth filter (eg: depth_lt=10) to avoid too deep output.

Packaging

I frequently use Hunter to figure out how distutils/setuptools work. It’s very hard to figure out what’s going on by just looking at the code - lots of stuff happens at runtime. If you ever tried to write a custom command you know what I mean.

To show everything that is being run:

PYTHONHUNTER='module_startswith=["setuptools", "distutils", "wheel"]' python setup.py bdist_wheel

If you want too see some interesting variables:

PYTHONHUNTER='module_startswith=["setuptools", "distutils", "wheel"], actions=[CodePrinter, VarsPrinter("self.bdist_dir")]' python setup.py bdist_wheel

Typical

Normally you’d only want to look at your code. For that purpose, there’s the stdlib option. Set it to False.

Building a bit on the previous example, if I have a build Distutils command and I only want to see my code then I’d run this:

PYTHONHUNTER='stdlib=False' python setup.py build

But this also means I’d be seeing anything from site-packages. I could filter on only the events from the current directory (assuming the filename is going to be a relative path):

PYTHONHUNTER='~Q(filename_startswith="/")' python setup.py build

Debugging a test

In tests it is convenient to ignore everything that is in stdlib and site-packages and start hunter right before the tested function.

from hunter import trace, Q
trace(Q(stdlib=False), ~Q(filename_contains='site-packages'))

It also helps to save output into a file to compare different runs. An example below uses pytest with -k option to select and tun a test or tests with string some in name. The output is then piped to testout1 file.

pytest test/test_simple.py -k some &> testout1

Needle in the haystack

If the needle might be though the stdlib then you got not choice. But some of the hay is very verbose and useless, like stuff from the re module.

Note that there are few “hidden” modules like sre, sre_parse, sre_compile etc. You can filter that out with:

~Q(module_regex="(re|sre.*)$")

Although filtering out that regex stuff can cut down lots of useless output you usually still get lots of output.

Another way, if you got at least some vague idea of what might be going on is to “grep” for sourcecode. Example, to show all the code that does something with a build_dir property:

source_contains=".build_dir"

You could even extend that a bit to dump some variables:

source_contains=".build_dir", actions=[CodePrinter, VarsPrinter("self.build_dir")]

Stop after N calls

Say you want to stop tracing after 1000 events, you’d do this:

~Q(calls_gt=1000, action=Stop)

Explanation:

Q(calls_gt=1000, action=Stop) will translate to When(Query(calls_gt=1000), Stop)

Q(calls_gt=1000) will return True when 1000 call count is hit.

When(something, Stop) will call Stop when something returns True. However it will also return the result of something - the net effect being nothing being shown up to 1000 calls. Clearly not what we want …

So then we invert the result, ~When(...) is the same as Not(When).

This may not seem intuitive but for now it makes internals simpler. If When would always return True then Or(When, When) would never run the second When and we’d need to have all sorts of checks for this. This may change in the future however.

“Probe” - lightweight tracing

Based on Robert Brewer’s FunctionProbe example.

The use-case is that you’d like to trace a huge application and running a tracer (even a cython one) would have a too great impact. To solve this you’d start the tracer only in placer where it’s actually needed.

To make this work you’d monkeypatch the function that needs the tracing. This example uses aspectlib:

def probe(qualname, *actions, **filters):
    def tracing_decorator(func):
        @functools.wraps(func)
        def tracing_wrapper(*args, **kwargs):
            # create the Tracer manually to avoid spending time in likely useless things like:
            # - loading PYTHONHUNTERCONFIG
            # - setting up the clear_env_var or thread_support options
            # - atexit cleanup registration
            with hunter.Tracer().trace(hunter.When(hunter.Query(**filters), *actions)):
                return func(*args, **kwargs)

        return tracing_wrapper

    aspectlib.weave(qualname, tracing_decorator)  # this does the monkeypatch

Suggested use:

• to get the regular tracing for that function:

  probe('module.func', hunter.VarsPrinter('var1', 'var2'))
  

• to log some variables at the end of the target function, and nothing deeper:

  probe('module.func', hunter.VarsPrinter('var1', 'var2'), kind="return", depth=0)
  

Another interesting thing is that you may note that you can reduce the implementation of the probe function down to just:

def probe(qualname, *actions, **kwargs):
    aspectlib.weave(qualname, functools.partial(hunter.wrap, actions=actions, **kwargs))

It will work the same, hunter.wrap being a decorator. However, while hunter.wrap offers the convenience of tracing just inside the target function (eg: probe('module.func', local=True)) it will also add a lot of extra filtering to trim irrelevant events from around the function (like return from tracer setup, and the internals of the decorator), in addition to what hunter.trace() does. Not exactly lightweight…

Silenced exception runtime analysis

Finding code that discards exceptions is sometimes really hard.

Note

This was made available in hunter.actions.ErrorSnooper for convenience. This cookbook entry will remain for educational purposes.

While this is easy to find with a grep "except:" -R .:

def silenced_easy():
    try:
        error()
    except:
        pass

Variants of this ain’t easy to grep:

def silenced_easy():
    try:
        error()
    except Exception:
        pass

If you can’t simply review all the sourcecode then runtime analysis is one way to tackle this:

class DumpExceptions(hunter.CodePrinter):
    events = ()
    depth = 0
    count = 0
    exc = None

    def __init__(self, max_count=10, **kwargs):
        self.max_count = max_count
        self.backlog = collections.deque(maxlen=5)
        super(DumpExceptions, self).__init__(**kwargs)

    def __call__(self, event):
        self.count += 1
        if event.kind == 'exception':  # something interesting happened ;)
            self.events = list(self.backlog)
            self.events.append(event.detach(self.try_repr))
            self.exc = self.try_repr(event.arg[1])
            self.depth = event.depth
            self.count = 0
        elif self.events:
            if event.depth > self.depth:  # too many details
                return
            elif event.depth < self.depth and event.kind == 'return':  # stop if function returned
                op = event.instruction
                op = op if isinstance(op, int) else ord(op)
                if op == RETURN_VALUE:
                    self.output("{BRIGHT}{fore(BLUE)}{} tracing {} on {}{RESET}\n",
                                ">" * 46, event.function, self.exc)
                    for event in self.events:
                        super(DumpExceptions, self).__call__(event)
                    if self.count > 10:
                        self.output("{BRIGHT}{fore(BLACK)}{} too many lines{RESET}\n",
                                    "-" * 46)
                    else:
                        self.output("{BRIGHT}{fore(BLACK)}{} function exit{RESET}\n",
                                    "-" * 46)
                self.events = []
                self.exc = None
            elif self.count < self.max_count:
                self.events.append(event.detach(self.try_repr))
        else:
            self.backlog.append(event.detach(self.try_repr))

Take note about the use of detach() and output().

Profiling

Hunter can be used to implement profiling (measure function timings).

The most basic implementation that only measures timings looks like this:

from hunter.actions import Action
from hunter.actions import RETURN_VALUE

class ProfileAction(Action):
    def __init__(self):
        self.timings = {}

    def __call__(self, event):
        if event.kind == 'call':
            self.timings[id(event.frame)] = time()
        elif event.kind == 'return':
            start_time = self.timings.pop(id(event.frame), None)
            if start_time is None:
                return
            delta = time() - start_time
            print(f'{event.function} returned: {event.arg}. Duration: {delta:.4f}s\n')

If you don’t care about exceptions at all this will be fine, but then you might just as well use a real profiler.

When exceptions occur Python send this to the tracer:

• event.kind="exception", event.arg=(exc_value, exc_type, tb)
  

• event.kind="return", event.arg=None
  

Unfortunately Python emits the return event even if the exception wasn’t discarded so we need to do some extra checks around the last bytecode instruction that run at the return event.

This means that we have to store the exception for a little while, and do the check at return:

from hunter.actions import Action
from hunter.actions import RETURN_VALUE

class ProfileAction(Action):
    def __init__(self):
        self.timings = {}

    def __call__(self, event):
        current_time = time()
        frame_id = id(event.frame)

        if event.kind == 'call':
            self.timings[frame_id] = current_time, None
        elif frame_id in self.timings:
            start_time, depth, exception = self.timings.pop(frame_id)

            if event.kind == 'exception':
                # store the exception
                # (there will be a followup 'return' event in which we deal with it)
                self.timings[frame_id] = start_time, event.arg
            elif event.kind == 'return':
                delta = current_time - start_time
                if event.instruction == RETURN_VALUE:
                    # exception was discarded
                    print(f'{event.function} returned: {event.arg}. Duration: {delta:.4f}s\n')
                else:
                    print(f'{event.function} raised exception: {exception}. Duration: {delta:.4f}s\n')

If you try that example you may notice that it’s not completely equivalent to any of the profilers available out there: data for builtin functions is missing.

Python does in fact have a profiling mode (eg: hunter.trace(profile=True) and that will make hunter use sys.setprofile instead of sys.setrace. However there are some downsides with that API:

• exception data will be missing (most likely because profiling is designed for speed and tracebacks are costly to build)
• trace events for builtin functions do not have their own frame objects (so we need to cater for that)

Behold, a ProfileAction that works in any mode:

from hunter.actions import ColorStreamAction
from hunter.actions import RETURN_VALUE

class ProfileAction(ColorStreamAction):
    # using ColorStreamAction brings this more in line with the other actions
    # (stream option, coloring and such, see the other examples for colors)
    def __init__(self, **kwargs):
        self.timings = {}
        super(ProfileAction, self).__init__(**kwargs)

    def __call__(self, event):
        current_time = time()
        # include event.builtin in the id so we don't have problems
        # with Python reusing frame objects from the previous call for builtin calls
        frame_id = id(event.frame), str(event.builtin)

        if event.kind == 'call':
            self.timings[frame_id] = current_time, None
        elif frame_id in self.timings:
            start_time, exception = self.timings.pop(frame_id)

            # try to find a complete function name for display
            function_object = event.function_object
            if event.builtin:
                function = '<builtin>.{}'.format(event.arg.__name__)
            elif function_object:
                if hasattr(function_object, '__qualname__'):
                    function = '{}.{}'.format(
                        function_object.__module__, function_object.__qualname__
                    )
                else:
                    function = '{}.{}'.format(
                        function_object.__module__,
                        function_object.__name__
                    )
            else:
                function = event.function

            if event.kind == 'exception':
                # store the exception
                # (there will be a followup 'return' event in which we deal with it)
                self.timings[frame_id] = start_time, event.arg
            elif event.kind == 'return':
                delta = current_time - start_time
                if event.instruction == RETURN_VALUE:
                    # exception was discarded
                    self.output(
                        '{fore(BLUE)}{} returned: {}. Duration: {:.4f}s{RESET}\n',
                        function, event.arg, delta
                    )
                else:
                    self.output(
                        '{fore(RED)}{} raised exception: {}. Duration: {:.4f}s{RESET}\n',
                        function, exception, delta
                    )

Reference

Helpers

hunter.trace(*predicates, **options)	Starts tracing.
hunter.stop()	Stop tracing.
hunter.wrap([function_to_trace])	Functions decorated with this will be traced.
hunter.And(*predicates, **kwargs)	Helper that flattens out predicates in a single hunter.predicates.And object if possible.
hunter.Backlog(*conditions, **kwargs)	Helper that merges kwargs and conditions prior to creating the Backlog.
hunter.From([condition, predicate, watermark])	Helper that converts keyword arguments to From(condition=Q(**normal_kwargs), predicate=Q(**rel_kwargs) where rel_kwargs are all the kwargs that start with “depth” or “calls”.
hunter.Not(*predicates, **kwargs)	Helper that flattens out predicates in a single hunter.predicates.And object if possible.
hunter.Or(*predicates, **kwargs)	Helper that flattens out predicates in a single hunter.predicates.Or object if possible.
hunter.Q(*predicates, **query)	Helper that handles situations where hunter.predicates.Query objects (or other callables) are passed in as positional arguments - it conveniently converts those to a hunter.predicates.And predicate.

Actions

hunter.actions.CallPrinter(*args, **kwargs)	An action that just prints the code being executed, but unlike hunter.CodePrinter it indents based on callstack depth and it also shows repr() of function arguments.
hunter.actions.CodePrinter([stream, …])	An action that just prints the code being executed.
hunter.actions.ColorStreamAction([stream, …])	Baseclass for your custom action.
hunter.actions.Debugger([klass])	An action that starts pdb.
hunter.actions.ErrorSnooper(*args, **kwargs)	An action that prints events around silenced exceptions.
hunter.actions.Manhole(**options)
hunter.actions.StackPrinter([depth, limit])	An action that prints a one-line stacktrace.
hunter.actions.VarsPrinter(*names, **options)	An action that prints local variables and optionally global variables visible from the current executing frame.
hunter.actions.VarsSnooper(**options)	A PySnooper-inspired action, similar to VarsPrinter, but only show variable changes.

Warning

The following (Predicates and Internals) have Cython implementations in modules prefixed with “_”. They should be imported from the hunter module, not hunter.something to be sure you get the best available implementation.

Predicates

hunter.predicates.And(*predicates)	Logical conjunction.
hunter.predicates.Backlog(condition[, size, …])	Until-point buffering mechanism.
hunter.predicates.From(condition[, …])	From-point filtering mechanism.
hunter.predicates.Not(predicate)	Logical complement (negation).
hunter.predicates.Or(*predicates)	Logical disjunction.
hunter.predicates.Query(**query)	Event-filtering predicate.
hunter.predicates.When(condition, *actions)	Conditional predicate.

Internals

hunter.event.Event(frame, kind, arg[, …])	A wrapper object for Frame objects.
hunter.tracer.Tracer([threading_support, …])	Tracer object.

---

Helpers

hunter.trace(*predicates, clear_env_var=False, action=CodePrinter, actions=[], **kwargs)

Starts tracing. Can be used as a context manager (with slightly incorrect semantics - it starts tracing before __enter__ is called).

Parameters:

*predicates (callables) – Runs actions if all of the given predicates match.

Keyword Arguments:  

• clear_env_var – Disables tracing in subprocess. Default: False.
• threading_support –

  Enable tracing new threads. Default: None.

  Modes:

  • None - automatic (enabled but actions only prefix with thread name if more than 1 thread)
  • False - completely disabled
  • True - enabled (actions always prefix with thread name)

  You can also use: threads_support, thread_support, threadingsupport, threadssupport, threadsupport, threading, threads or thread.

• action – Action to run if all the predicates return True. Default: CodePrinter.
• actions – Actions to run (in case you want more than 1).
• **kwargs – for convenience you can also pass anything that you’d pass to hunter.Q

See also

hunter.tracer.Tracer or hunter.event.Event

hunter.stop()

Stop tracing. Restores previous tracer (if there was any).

hunter.wrap(function_to_trace=None, **trace_options)

Functions decorated with this will be traced.

Use local=True to only trace local code, eg:

@hunter.wrap(local=True)
def my_function():
    ...

Keyword arguments are allowed, eg:

@hunter.wrap(action=hunter.CallPrinter)
def my_function():
    ...

Or, filters:

@hunter.wrap(module='foobar')
def my_function():
    ...

hunter.And(*predicates, **kwargs)

Helper that flattens out predicates in a single hunter.predicates.And object if possible. As a convenience it converts kwargs to a single hunter.predicates.Query instance.

Parameters:

• *predicates (callables) – Callables that returns True/False or hunter.predicates.Query objects.
• **kwargs – Arguments that may be passed to hunter.predicates.Query.

Returns: A hunter.predicates.And instance.

See also

hunter.predicates.And

hunter.Backlog(*conditions, **kwargs)

Helper that merges kwargs and conditions prior to creating the Backlog.

Parameters:

• *conditions (callable) – Optional Query object or a callable that returns True/False.
• size (int) – Number of events that the backlog stores. Effectively this is the maxlen for the internal deque.
• stack (int) – Stack size to fill. Setting this to 0 disables creating fake call events.
• vars (bool) – Makes global/local variables available in the stored events. This is an expensive option - it will use action.try_repr on all the variables.
• strip (bool) – If this option is set then the backlog will be cleared every time an event matching the condition is found. Disabling this may show more context every time an event matching the condition is found but said context may also be duplicated across multiple matches.
• action (ColorStreamAction) – A ColorStreamAction to display the stored events when an event matching the condition is found.
• filter (callable) – Optional Query object or a callable that returns True/False to filter the stored events with.
• **kwargs – Arguments that are passed to hunter.Q(). Any kwarg that starts with “depth” or “calls” will be included predicate.

See also

hunter.predicates.Backlog

hunter.From(condition=None, predicate=None, watermark=0, **kwargs)

Helper that converts keyword arguments to From(condition=Q(**normal_kwargs), predicate=Q(**rel_kwargs) where rel_kwargs are all the kwargs that start with “depth” or “calls”.

Parameters:

• condition (callable) – A callable that returns True/False or a hunter.predicates.Query object.
• predicate (callable) – Optional callable that returns True/False or a hunter.predicates.Query object to run after condition first returns True.
• **kwargs – Arguments that are passed to hunter.Q(). Any kwarg that starts with “depth” or “calls” will be included predicate.

Examples

From(function='foobar', depth_lt=5) coverts to From(Q(function='foobar'), Q(depth_lt=5)). The depth filter is moved in the predicate because it would not have any effect as a condition - it stop being called after it returns True, thus it doesn’t have the intended effect (a limit to how deep to trace from foobar).

See also

hunter.predicates.From

hunter.Not(*predicates, **kwargs)

Helper that flattens out predicates in a single hunter.predicates.And object if possible. As a convenience it converts kwargs to multiple hunter.predicates.Query instances.

Parameters:

• *predicates (callables) – Callables that returns True/False or hunter.predicates.Query objects.
• **kwargs – Arguments that may be passed to hunter.predicates.Query.

Returns: A hunter.predicates.Not instance (possibly containing a hunter.predicates.And instance).

See also

hunter.predicates.Not

hunter.Or(*predicates, **kwargs)

Helper that flattens out predicates in a single hunter.predicates.Or object if possible. As a convenience it converts kwargs to multiple hunter.predicates.Query instances.

Parameters:

• *predicates (callables) – Callables that returns True/False or hunter.predicates.Query objects.
• **kwargs – Arguments that may be passed to hunter.predicates.Query.

Returns: A hunter.predicates.Or instance.

See also

hunter.predicates.Or

hunter.Q(*predicates, **query)

Helper that handles situations where hunter.predicates.Query objects (or other callables) are passed in as positional arguments - it conveniently converts those to a hunter.predicates.And predicate.

See also

hunter.predicates.Query

---

Actions

class hunter.actions.CallPrinter(stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

An action that just prints the code being executed, but unlike hunter.CodePrinter it indents based on callstack depth and it also shows repr() of function arguments.

Parameters:

• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

New in version 1.2.0.

__call__(event)

Handle event and print filename, line number and source code. If event.kind is a return or exception also prints values.

__init__(*args, **kwargs)

Initialize self. See help(type(self)) for accurate signature.

class hunter.actions.CodePrinter(stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

An action that just prints the code being executed.

Parameters:

• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

__call__(event)

Handle event and print filename, line number and source code. If event.kind is a return or exception also prints values.

class hunter.actions.ColorStreamAction(stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

Baseclass for your custom action. Just implement your own __call__.

__eq__(other)

Return self==value.

__init__(stream=None, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

Initialize self. See help(type(self)) for accurate signature.

__repr__()

Return repr(self).

__str__()

Return str(self).

filename_prefix(event=None)

Get an aligned and trimmed filename prefix for the given event.

Returns: string

output(format_str, *args, **kwargs)

Write format_str.format(*args, **ANSI_COLORS, **kwargs) to self.stream.

For ANSI coloring you can place these in the format_str:

• {BRIGHT}
• {DIM}
• {NORMAL}
• {RESET}
• {fore(BLACK)}
• {fore(RED)}
• {fore(GREEN)}
• {fore(YELLOW)}
• {fore(BLUE)}
• {fore(MAGENTA)}
• {fore(CYAN)}
• {fore(WHITE)}
• {fore(RESET)}
• {back(BLACK)}
• {back(RED)}
• {back(GREEN)}
• {back(YELLOW)}
• {back(BLUE)}
• {back(MAGENTA)}
• {back(CYAN)}
• {back(WHITE)}
• {back(RESET)}

Parameters:

• format_str – a PEP-3101 format string
• *args
• **kwargs

Returns: string

pid_prefix()

Get an aligned and trimmed pid prefix.

thread_prefix(event)

Get an aligned and trimmed thread prefix for the given event.

try_repr(obj)

Safely call self.repr_func(obj). Failures will have special colored output and output is trimmed according to self.repr_limit.

Returns: string

try_source(event, full=False)

Get a failure-colorized source for the given event.

Return: string

try_str(obj)

Safely call str(obj). Failures will have special colored output and output is trimmed according to self.repr_limit.

Only used when dumping detached events.

Returns: string

class hunter.actions.Debugger(klass=pdb.Pdb, **kwargs)

An action that starts pdb.

__call__(event)

Runs a pdb.set_trace at the matching frame.

__eq__(other)

Return self==value.

__init__(klass=<class 'pdb.Pdb'>, **kwargs)

Initialize self. See help(type(self)) for accurate signature.

__repr__()

Return repr(self).

__str__()

Return str(self).

class hunter.actions.ErrorSnooper(max_events=50, max_depth=1, stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

An action that prints events around silenced exceptions. Note that it inherits the output of CodePrinter so no fancy call indentation.

Warning

Should be considered experimental. May show lots of false positives especially if you’re tracing lots of clumsy code like:

try:
    stuff = something[key]
except KeyError:
    stuff = "default"

Parameters:

• max_backlog (int) – Maximum number of events to record and display before the silenced exception is raised. Set to 0 to disable and get a speed boost. Default: 10.
• max_events (int) – Maximum number of events to record and display for each detected silenced exception. Default: 50.
• max_depth (int) – Increase if you want to drill into subsequent calls after an exception is raised. If you increase this you might want to also increase max_events since subsequent calls may have so many events you won’t get to see the return event. Default: 0 (doesn’t drill into any calls).
• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

New in version 3.1.0.

__call__(event)

Handle event and print filename, line number and source code. If event.kind is a return or exception also prints values.

__init__(*args, **kwargs)

Initialize self. See help(type(self)) for accurate signature.

class hunter.actions.Manhole(**options)

__call__(event)

Call self as a function.

__eq__(other)

Return self==value.

__init__(**options)

Initialize self. See help(type(self)) for accurate signature.

__repr__()

Return repr(self).

__str__()

Return str(self).

class hunter.actions.StackPrinter(depth=15, limit=2, stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

An action that prints a one-line stacktrace.

Parameters:

• depth (int) – The maximum number of frames to show.
• limit (int) – The maximum number of components to show in path. Eg: limit=2 means it will show 1 parent: foo/bar.py.
• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

__call__(event)

Handle event and print the stack.

__init__(depth=15, limit=2, **options)

Initialize self. See help(type(self)) for accurate signature.

class hunter.actions.VarsPrinter(name, [name, [name, [..., ]]]stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

An action that prints local variables and optionally global variables visible from the current executing frame.

Parameters:

• *names (strings) – Names to evaluate. Expressions can be used (will only try to evaluate if all the variables are present on the frame.
• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

__call__(event)

Handle event and print the specified variables.

__init__(*names, **options)

Initialize self. See help(type(self)) for accurate signature.

class hunter.actions.VarsSnooper(stream=sys.stderr, force_colors=False, force_pid=False, filename_alignment=40, thread_alignment=12, pid_alignment=9, repr_limit=1024, repr_func='safe_repr')

A PySnooper-inspired action, similar to VarsPrinter, but only show variable changes.

Warning

Should be considered experimental. Use judiciously.

• It stores reprs for all seen variables, therefore it can use lots of memory.
• Will leak memory if you filter the return events (eg: ~Q(kind="return")).
• Not thoroughly tested. May misbehave on code with closures/nonlocal variables.

Parameters:

• stream (file-like) – Stream to write to. Default: sys.stderr.
• filename_alignment (int) – Default size for the filename column (files are right-aligned). Default: 40.
• force_colors (bool) – Force coloring. Default: False.
• repr_limit (bool) – Limit length of repr() output. Default: 512.
• repr_func (string or callable) – Function to use instead of repr. If string must be one of ‘repr’ or ‘safe_repr’. Default: 'safe_repr'.

__call__(event)

Handle event and print the specified variables.

__init__(**options)

Initialize self. See help(type(self)) for accurate signature.

---

Predicates

Warning

These have Cython implementations in modules prefixed with “_”.

Note that:

• Every predicate except When has a helper importable directly from the hunter package.
• Ideally you’d use the helpers instead of these to get the best available implementation, extra validation and better argument handling.

class hunter.predicates.And(*predicates)

Logical conjunction. Returns False at the first sub-predicate that returns False, otherwise returns True.

__and__(other)

Convenience API so you can do And(...) & other. It converts that to And(..., other).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(*predicates)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~And(...). It converts that to Not(And(...)).

__or__(other)

Convenience API so you can do And(...) | other. It converts that to Or(And(...), other).

__rand__(other)

Convenience API so you can do other & And(...). It converts that to And(other, And(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | And(...). It converts that to Or(other, And(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

class hunter.predicates.Backlog(condition, size=100, stack=10, vars=False, strip=True, action=None, filter=None)

Until-point buffering mechanism. It will buffer detached events up to the given size and display them using the given action when condition returns True.

This is a complement to From - essentially working the other way. While From shows events after something interesting occurred the Backlog will show events prior to something interesting occurring.

If the depth delta from the first event in the backlog and the event that matched the condition is less than the given stack then it will create fake call events to be passed to the action before the events from the backlog are passed in.

Using a filter or pre-filtering is recommended to reduce storage work and improve tracing speed. Pre-filtering means that you use Backlog inside a When or :class:`~hunter.And - effectively reducing the number of Events that get to the Backlog.

Parameters:

• condition (callable) – Optional Query object or a callable that returns True/False.
• size (int) – Number of events that the backlog stores. Effectively this is the maxlen for the internal deque.
• stack (int) – Stack size to fill. Setting this to 0 disables creating fake call events.
• vars (bool) – Makes global/local variables available in the stored events. This is an expensive option - it will use action.try_repr on all the variables.
• strip (bool) – If this option is set then the backlog will be cleared every time an event matching the condition is found. Disabling this may show more context every time an event matching the condition is found but said context may also be duplicated across multiple matches.
• action (ColorStreamAction) – A ColorStreamAction to display the stored events when an event matching the condition is found.
• filter (callable) – Optional Query object or a callable that returns True/False to filter the stored events with.

See also

hunter.predicates.From

__and__(other)

Convenience API so you can do Backlog(...) & other. It converts that to And(Backlog(...), other)).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(condition, size=100, stack=10, vars=False, strip=True, action=None, filter=None)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~Backlog(...). It converts that to Not(Backlog(...)).

__or__(other)

Convenience API so you can do Backlog(...) | other. It converts that to Or(Backlog(...), other).

__rand__(other)

Convenience API so you can do other & Backlog(...). It converts that to And(other, Backlog(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | Backlog(...). It converts that to Or(other, Backlog(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

filter(*predicates, **kwargs)

Returns another Backlog instance with extra output filtering. If the current instance already have filters they will be merged by using an And predicate.

Parameters:

• *predicates (callables) – Callables that returns True/False or Query objects.
• **kwargs – Arguments that may be passed to Query.

Returns: A new Backlog instance.

class hunter.predicates.From(condition, predicate=None, watermark=0)

From-point filtering mechanism. Switches on to running the predicate after condition matches, and switches off when the depth goes lower than the initial level.

After condition(event) returns True the event.depth will be saved and calling this object with an event will return predicate(event) until event.depth - watermark is equal to the depth that was saved.

Parameters:

• condition (callable) – Optional Query object or a callable that returns True/False.
• predicate (callable) – Optional Query object or a callable that returns True/False to run after condition first returns True. Note that this predicate will be called with a event-copy that has adjusted depth and calls to the initial point where the condition matched. In other words they will be relative.
• watermark (int) – Depth difference to switch off and wait again on condition.

See also

hunter.predicates.Backlog

__and__(other)

Convenience API so you can do From(...) & other. It converts that to And(From(...), other)).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(condition, predicate=None, watermark=0)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~From(...). It converts that to Not(From(...)).

__or__(other)

Convenience API so you can do From(...) | other. It converts that to Or(From(...), other).

__rand__(other)

Convenience API so you can do other & From(...). It converts that to And(other, From(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | From(...). It converts that to Or(other, From(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

class hunter.predicates.Not(predicate)

Logical complement (negation). Simply returns not predicate(event).

__and__(other)

Convenience API so you can do Not(...) & other. It converts that to And(Not(...), other).

Note that Not(...) & Not(...) converts to Not(Or(..., ...)).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(predicate)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~Not(...). It converts that to ....

__or__(other)

Convenience API so you can do Not(...) | other. It converts that to Or(Not(...), other).

Note that Not(...) | Not(...) converts to Not(And(..., ...)).

__rand__(other)

Convenience API so you can do other & Not(...). It converts that to And(other, Not(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | Not(...). It converts that to Or(other, Not(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

class hunter.predicates.Or(*predicates)

Logical disjunction. Returns True after the first sub-predicate that returns True.

__and__(other)

Convenience API so you can do Or(...) & other. It converts that to And(Or(...), other).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(*predicates)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~Or(...). It converts that to Not(Or(...)).

__or__(other)

Convenience API so you can do Or(...) | other. It converts that to Or(..., other).

__rand__(other)

Convenience API so you can do other & Or(...). It converts that to And(other, Or(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | Or(...). It converts that to Or(other, Or(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

class hunter.predicates.Query(**query)

Event-filtering predicate.

See hunter.event.Event for details about the fields that can be filtered on.

Parameters:

query – criteria to match on.

Accepted arguments: arg, builtin, calls, code, depth, filename, frame, fullsource, function, globals, kind, lineno, locals, module, source, stdlib, threadid, threadname.

__and__(other)

Convenience API so you can do Query(...) & Query(...). It converts that to And(Query(...), Query(...)).

__call__(event)

Handles event. Returns True if all criteria matched.

__eq__(other)

Return self==value.

__init__(**query)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~Query(...). It converts that to Not(Query(...)).

__or__(other)

Convenience API so you can do Query(...) | Query(...). It converts that to Or(Query(...), Query(...)).

__rand__(other)

Convenience API so you can do other & Query(...). It converts that to And(other, Query(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | Query(...). It converts that to Or(other, Query(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

class hunter.predicates.When(condition, *actions)

Conditional predicate. Runs actions when condition(event) is True.

Actions take a single event argument.

__and__(other)

Convenience API so you can do When(...) & other. It converts that to And(When(...), other).

__call__(event)

Handles the event.

__eq__(other)

Return self==value.

__init__(condition, *actions)

Initialize self. See help(type(self)) for accurate signature.

__invert__()

Convenience API so you can do ~When(...). It converts that to Not(When(...)).

__or__(other)

Convenience API so you can do When(...) | other. It converts that to Or(When(...), other).

__rand__(other)

Convenience API so you can do other & When(...). It converts that to And(other, When(...)).

__repr__()

Return repr(self).

__ror__(other)

Convenience API so you can do other | When(...). It converts that to Or(other, When(...)).

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

---

Internals

Warning

These have Cython implementations in modules prefixed with “_”. They should be imported from the hunter module, not hunter.something to be sure you get the best available implementation.

Normally these are not used directly. Perhaps just the Tracer may be used directly for performance reasons.

class hunter.event.Event(frame, kind, arg, tracer=None, depth=None, calls=None, threading_support=?)

A wrapper object for Frame objects. Instances of this are passed to your custom functions or predicates.

Provides few convenience properties.

Parameters:

• frame (Frame) – A python Frame object.
• kind (str) – A string like 'call', 'line', 'return' or 'exception'.
• arg – A value that depends on kind. Usually is None but for 'return' or 'exception' other values may be expected.
• tracer (hunter.tracer.Tracer) – The Tracer instance that created the event. Needed for the calls and depth fields.

__eq__(other)

Return self==value.

__getitem__

Return getattr(self, name).

__init__(frame, kind, arg, tracer=None, depth=None, calls=None, threading_support=?)

Initialize self. See help(type(self)) for accurate signature.

__repr__()

Return repr(self).

__weakref__

list of weak references to the object (if defined)

arg = None

A value that depends on kind

builtin = None

If kind of the event is one of 'c_call', 'c_return', or 'c_exception' then this will be True.

Type:bool

calls = None

A counter for total number of calls up to this Event.

Type:int

code

A code object (not a string).

depth = None

Tracing depth (increases on calls, decreases on returns).

Type:int

detach(value_filter=None)

Return a copy of the event with references to live objects (like the frame) removed. You should use this if you want to store or use the event outside the handler.

You should use this if you want to avoid memory leaks or side-effects when storing the events.

Parameters:

value_filter – Optional callable that takes one argument: value.

If not specified then the arg, globals and locals fields will be None.

Example usage in a ColorStreamAction subclass:

def __call__(self, event):
    self.events = [event.detach(lambda field, value: self.try_repr(value))]

detached = None

Flag that is True if the event was created with detach().

Type:bool

filename

A string with the path to the module’s file. May be empty if __file__ attribute is missing. May be relative if running scripts.

Type:str

frame = None

The original Frame object.

Note

Not allowed in the builtin predicates (it’s the actual Frame object). You may access it from your custom predicate though.

fullsource

A string with the sourcecode for the current statement (from linecache - failures are ignored).

May include multiple lines if it’s a class/function definition (will include decorators).

Type:str

function

A string with function name.

Type:str

function_object

The function instance.

Warning

Use with prudence.

• Will be None for decorated functions on Python 2 (methods may still work tho).
• May be None if tracing functions or classes not defined at module level.
• May be very slow if tracing modules with lots of variables.

Type:function or None

globals

A dict with global variables.

Type:dict

instruction

Last byte instruction. If no bytecode was used (Cython code) then it returns None. Depending on Python version it might be an int or a single char string.

Type:int or single char string or None

kind = None

The kind of the event, could be one of 'call', 'line', 'return', 'exception'.

Type:str

lineno

An integer with line number in file.

Type:int

locals

A dict with local variables.

Type:dict

module

A string with module name (like 'foo.bar').

Type:str

source

A string with the sourcecode for the current line (from linecache - failures are ignored).

Fast but sometimes incomplete.

Type:str

stdlib

A boolean flag. True if frame is in stdlib.

Type:bool

threadid

Current thread ident. If current thread is main thread then it returns None.

Type:int or None

threading_support = None

A copy of the hunter.tracer.Tracer.threading_support flag.

Note

Not allowed in the builtin predicates. You may access it from your custom predicate though.

Type:bool or None

threadname

Current thread name.

Type:str

class hunter.tracer.Tracer(threading_support=None, profiling_mode=False)

Tracer object.

Parameters:threading_support (bool) – Hooks the tracer into threading.settrace as well if True.

__call__(frame, kind, arg)

The settrace function.

Note

This always returns self (drills down) - as opposed to only drilling down when predicate(event) is True because it might match further inside.

__enter__()

Does nothing. Users are expected to call trace().

Returns: self

__exit__(exc_type, exc_val, exc_tb)

Wrapper around stop(). Does nothing with the arguments.

__init__(threading_support=None, profiling_mode=False)

Initialize self. See help(type(self)) for accurate signature.

__repr__()

Return repr(self).

__weakref__

list of weak references to the object (if defined)

calls = None

A counter for total number of ‘call’ frames that this Tracer went through.

Type:int

depth = None

Tracing depth (increases on calls, decreases on returns)

Type:int

handler

The current predicate. Set via hunter.Tracer.trace().

previous

The previous tracer, if any (whatever sys.gettrace() returned prior to hunter.Tracer.trace()).

profiling_mode = None

True if profiling mode was enabled. Should be considered read-only.

Type:bool

stop()

Stop tracing. Reinstalls the previous tracer.

threading_support = None

True if threading support was enabled. Should be considered read-only.

Type:bool

trace(predicate)

Starts tracing with the given callable.

Parameters:predicate (callable that accepts a single Event argument) Returns:self

Contributing

Contributions are welcome, and they are greatly appreciated! Every little bit helps, and credit will always be given.

Bug reports

When reporting a bug please include:

• Your operating system name and version.
• Any details about your local setup that might be helpful in troubleshooting.
• Detailed steps to reproduce the bug.

Documentation improvements

Hunter could always use more documentation, whether as part of the official Hunter docs, in docstrings, or even on the web in blog posts, articles, and such.

Feature requests and feedback

The best way to send feedback is to file an issue at https://github.com/ionelmc/python-hunter/issues.

If you are proposing a feature:

• Explain in detail how it would work.
• Keep the scope as narrow as possible, to make it easier to implement.
• Remember that this is a volunteer-driven project, and that code contributions are welcome :)

Development

To set up python-hunter for local development:

1. Fork python-hunter (look for the “Fork” button).

2. Clone your fork locally:

   git clone git@github.com:YOURGITHUBNAME/python-hunter.git
   

3. Create a branch for local development:

   git checkout -b name-of-your-bugfix-or-feature
   

   Now you can make your changes locally.

4. When you’re done making changes run all the checks and docs builder with tox one command:

   tox
   

5. Commit your changes and push your branch to GitHub:

   git add .
   git commit -m "Your detailed description of your changes."
   git push origin name-of-your-bugfix-or-feature
   

6. Submit a pull request through the GitHub website.

Pull Request Guidelines

If you need some code review or feedback while you’re developing the code just make the pull request.

For merging, you should:

1. Include passing tests (run tox).
2. Update documentation when there’s new API, functionality etc.
3. Add a note to CHANGELOG.rst about the changes.
4. Add yourself to AUTHORS.rst.

Tips

To run a subset of tests:

tox -e envname -- pytest -k test_myfeature

To run all the test environments in parallel:

tox -p auto

Authors

• Ionel Cristian Mărieș - https://blog.ionelmc.ro
• Claudiu Popa - https://github.com/PCManticore
• Mikhail Borisov - https://github.com/borman
• Dan Ailenei - https://github.com/Dan-Ailenei
• Tom Schraitle - https://github.com/tomschr

Changelog

3.5.2 (2022-10-26)

• Added Python 3.11 wheels.

3.5.1 (2022-09-27)

• Fixed breakage in hunter-trace when Ctrl-C.

3.5.0 (2022-09-11)

• Add support for generators and coroutines in the hunter.wrap decorator.
• Dropped support for Python 3.6.

3.4.3 (2021-12-15)

• Removed most of the Python 2 support code.
• Fix some refactoring regression in setup.py and make the 3.4.x series installable only on Python 3.6 and later.
• Yank 3.4.0, 3.4.1, 3.4.2 releases to avoid install problems on Python 2.7.

3.4.2 (2021-12-15)

• Fixed CI to properly make win32 wheels.

3.4.1 (2021-12-14)

• Add support for building a pp37.pp38 tagged wheel (basically an universal wheel installable just for those two PyPy versions).

3.4.0 (2021-12-14)

• Switched CI to GitHub Actions, this has a couple consequences:
  • Support for Python 2.7 is dropped. You can still install it there but it’s not tested anymore and Python 2 specific handling will be removed at some point.
  • Linux wheels are now provided in musllinux and manylinux2014 variants.
• Extension building is now completely skipped on PyPy.
• A pure but tagged as platform specific wheel is now provided for PyPy (to have fast installs there as well).

3.3.8 (2021-06-23)

• Fixed CI problem that publishes same type of wheels two times.

3.3.7 (2021-06-23)

• Fixed a bug with how stdlib is detected on Windows (at least).

3.3.6 (2021-06-23)

• Fixed regression from 3.3.4: stdlib filter was broken.
• Improved the pth file (PYTHONHUNTER environment variable activation) to use a clean eval environment. No bogus variables like line (from the site.py machinery) will be available anymore.
• Fixed a bug in VarsSnooper that would make it fail in rare situation where a double return event is emitted.

3.3.5 (2021-06-11)

• Added support for Python 3.10.
• Added support for time objects and the fold option in safe_repr.
• 3.3.4 was skipped cause I messed up the CI.

3.3.3 (2021-05-04)

• Fixed tracer still being active for other threads after it was stopped.

  Python unfortunately only allows removing the trace function for the current thread - now Tracer will uninstall itself if it’s marked as stopped.

  This fixes bogus errors that appear when using ipdb with the hunter.actions.Debugger action while thread support is enabled (the default).

3.3.2 (2021-03-25)

• Changed CI to build Python 3.9 wheels. Python 3.5 no longer tested and wheels no longer built to keep things simple.
• Documentation improvements.

3.3.1 (2020-10-24)

• Fixed CI/test issues that prevented all of 21 wheels being published.

3.3.0 (2020-10-23)

• Fixed handling so that hunter.event.Event.module is always the "?" string instead of None. Previously it was None when tracing particularly broken code and broke various predicates.
• Similarly hunter.event.Event.filename is now "?" if there’s no filename available.
• Building on the previous changes the actions have simpler code for displaying missing module/filenames.
• Changed hunter.actions.CallPrinter so that trace events for builtin functions are displayed differently. These events appear when using profile mode (eg: trace(profile=True)).
• Fixed failure that could occur if hunter.event.Event.module is an unicode string. Now it’s always a regular string. Only applies to Python 2.
• Fixed argument display when tracing functions with tuple arguments. Closes #88. Only applies to Python 2.
• Improved error reporting when internal failures occur. Now some details about the triggering event are logged.

3.2.2 (2020-09-04)

• Fixed oversight over what value is in hunter.event.Event.builtin. Now it’s always a boolean, and can be used consistently in filters (eg: builtin=True,function='getattr').

3.2.1 (2020-08-18)

• Added support for regex, date and datetime in safe_repr.
• Fixed call argument display when positional and keyword arguments are used in hunter.actions.CallPrinter.

3.2.0 (2020-08-16)

• Implemented the StackPrinter action.
• Implemented the Backlog predicate. Contributed by Dan Ailenei in #81.
• Improved contributing section in docs a bit. Contributed by Tom Schraitle in #85.
• Improved filtering performance by avoiding a lot of unnecessary PyObject_GetAttr calls in the Cython implementation of Backlog.
• Implemented the ErrorSnooper action.
• Added support for profiling mode (eg: trace(profile=True)). This mode will use setprofile instead of settrace.
• Added ARM64 wheels and CI.
• Added hunter.event.Event.instruction and hunter.event.Event.builtin (usable in profile mode).
• Added more cookbook entries.

3.1.3 (2020-02-02)

• Improved again the stdlib check to handle certain paths better.

3.1.2 (2019-01-19)

• Really fixed the <frozen importlib.something stdlib check.

3.1.1 (2019-01-19)

• Marked all the <frozen importlib.something files as part of stdlib.

3.1.0 (2019-01-19)

• Added ErrorSnooper - an action that detects silenced exceptions.
• Added load_config() and fixed issues with configuration being loaded too late from the PYTHONHUNTERCONFIG environment variable.
• Changed From() helper to automatically move depth and calls filters to the predicate (so they filter after From activates).
• Changed From to pass a copy of event to the predicate. The copy will have the depth and calls attributes adjusted to the point where From activated.
• Fixed a bunch of inconsistencies and bugs when using & and | operators with predicates.
• Fixed a bunch of broken fields on detached events (function_object and arg).
• Improved docstrings in various and added a configuration doc section.
• Improved testing (more coverage).

3.0.5 (2019-12-06)

• Really fixed safe_repr so it doesn’t cause side-effects (now isinstance/issubclass are avoided - they can cause side-effects in code that abuses descriptors in special attributes/methods).

3.0.4 (2019-10-26)

• Really fixed stream setup in actions (using force_colors without any stream was broken). See: ColorStreamAction.
• Fixed __repr__ for the From predicate to include watermark.
• Added binary wheels for Python 3.8.

3.0.3 (2019-10-13)

• Fixed safe_repr on pypy so it’s safer on method objects. See: ColorStreamAction.

3.0.2 (2019-10-10)

• Fixed setting stream from PYTHONHUNTERCONFIG environment variable. See: ColorStreamAction.
• Fixed a couple minor documentation issues.

3.0.1 (2019-06-17)

• Fixed issue with coloring missing source message (coloring leaked into next line).

3.0.0 (2019-06-17)

• The package now uses setuptools-scm for development builds (available at https://test.pypi.org/project/hunter/). As a consequence installing the sdist will download setuptools-scm.

• Recompiled cython modules with latest Cython. Hunter can be installed without any Cython, as before.

• Refactored some of the cython modules to have more typing information and not use deprecated property syntax.

• Replaced unsafe_repr option with repr_func. Now you can use your custom repr function in the builtin actions. BACKWARDS INCOMPATIBLE

• Fixed buggy filename handling when using Hunter in ipython/jupyter. Source code should be properly displayed now.

• Removed globals option from VarsPrinter action. Globals are now always looked up. BACKWARDS INCOMPATIBLE

• Added support for locals in VarsPrinter action. Now you can do VarsPrinter('len(foobar)').

• Always pass module_globals dict to linecache methods. Source code from PEP-302 loaders is now printed properly. Contributed by Mikhail Borisov in #65.

• Various code cleanup, style and docstring fixing.

• Added hunter.From() helper to allow passing in filters directly as keyword arguments.

• Added hunter.event.Event.detach() for storing events without leaks or side-effects (due to prolonged references to Frame objects, local or global variables).

• Refactored the internals of actions for easier subclassing.

  Added the filename_prefix(), output(), pid_prefix(), thread_prefix(), try_repr() and try_source() methods to the hunter.actions.ColorStreamAction baseclass.

• Added hunter.actions.VarsSnooper - a PySnooper-inspired variant of VarsPrinter. It will record and show variable changes, with the risk of leaking or using too much memory of course :)

• Fixed tracers to log error and automatically stop if there’s an internal failure. Previously error may have been silently dropped in some situations.

2.2.1 (2019-01-19)

• Fixed a link in changelog.
• Fixed some issues in the Travis configuration.

2.2.0 (2019-01-19)

• Added hunter.predicates.From predicate for tracing from a specific point. It stop after returning back to the same call depth with a configurable offset.
• Fixed PYTHONHUNTERCONFIG not working in some situations (config values were resolved at the wrong time).
• Made tests in CI test the wheel that will eventually be published to PyPI (tox-wheel).
• Made event.stdlib more reliable: pkg_resources is considered part of stdlib and few more paths will be considered as stdlib.
• Dumbed down the get_peercred check that is done when attaching with hunter-trace CLI (via hunter.remote.install()). It will be slightly insecure but will work on OSX.
• Added OSX in the Travis test grid.

2.1.0 (2018-11-17)

• Made threading_support on by default but output automatic (also, now 1 or 0 allowed).
• Added pid_alignment and force_pid action options to show a pid prefix.
• Fixed some bugs around __eq__ in various classes.
• Dropped Python 3.3 support.
• Dropped dependency on fields.
• Actions now repr using a simplified implementation that tries to avoid calling __repr__ on user classes in order to avoid creating side-effects while tracing.
• Added support for the PYTHONHUNTERCONFIG environment variable (stores defaults and doesn’t activate hunter).

2.0.2 (2017-11-24)

• Fixed indentation in hunter.actions.CallPrinter action (shouldn’t deindent on exception).
• Fixed option filtering in Cython Query implementation (filtering on tracer was allowed by mistake).
• Various fixes to docstrings and docs.

2.0.1 (2017-09-09)

• Now Py_AddPendingCall is used instead of acquiring the GIL (when using GDB).

2.0.0 (2017-09-02)

• Added the hunter.event.Event.count and hunter.event.Event.calls attributes.
• Added the lt/lte/gt/gte lookups.
• Added convenience aliases for startswith (sw), endswith (ew), contains (has) and regex (rx).
• Added a convenience hunter.wrap() decorator to start tracing around a function.
• Added support for remote tracing (with two backends: manhole and GDB) via the hunter-trace bin. Note: Windows is NOT SUPPORTED.
• Changed the default action to hunter.actions.CallPrinter. You’ll need to use action=CodePrinter if you want the old output.

1.4.1 (2016-09-24)

• Fix support for getting sources for Cython module (it was broken on Windows and Python3.5+).

1.4.0 (2016-09-24)

• Added support for tracing Cython modules (#30). A # cython: linetrace=True stanza or equivalent is required in Cython modules for this to work.

1.3.0 (2016-04-14)

• Added hunter.event.Event.thread.
• Added hunter.event.Event.threadid and hunter.event.Event.threadname (available for filtering with hunter.Q()).
• Added hunter.event.Event.threading_support argument to hunter.trace(). It makes new threads be traced and changes action output to include thread name.
• Added support for using pdb++ in the hunter.actions.Debugger action.
• Added support for using manhole via a new hunter.actions.Manhole action.
• Made the hunter.event.Event.handler a public but readonly property.

1.2.2 (2016-01-28)

• Fix broken import. Require fields>=4.0.
• Simplify a string check in Cython code.

1.2.1 (2016-01-27)

• Fix “KeyError: ‘normal’” bug in hunter.actions.CallPrinter. Create the NO_COLORS dict from the COLOR dicts. Some keys were missing.

1.2.0 (2016-01-24)

• Fixed printouts of objects that return very large string in __repr__(). Trimmed to 512. Configurable in actions with the repr_limit option.
• Improved validation of hunter.actions.VarsPrinter’s initializer.
• Added a hunter.actions.CallPrinter action.

1.1.0 (2016-01-21)

• Implemented a destructor (__dealloc__) for the Cython tracer.
• Improved the restoring of the previous tracer in the Cython tracer (use PyEval_SetTrace) directly.
• Removed tracer as an allowed filtering argument in hunter.Query.
• Add basic validation (must be callable) for positional arguments and actions passed into hunter.Q. Closes #23.
• Fixed stdlib checks (wasn’t very reliable). Closes #24.

1.0.2 (2016-01-05)

• Fixed missing import in setup.py.

1.0.1 (2015-12-24)

• Fix a compile issue with the MSVC compiler (seems it don’t like the inline option on the fast_When_call).

1.0.0 (2015-12-24)

• Implemented fast tracer and query objects in Cython. MAY BE BACKWARDS INCOMPATIBLE

  To force using the old pure-python implementation set the PUREPYTHONHUNTER environment variable to non-empty value.

• Added filtering operators: contains, startswith, endswith and in. Examples:

  • Q(module_startswith='foo' will match events from foo, foo.bar and foobar.
  • Q(module_startswith=['foo', 'bar'] will match events from foo, foo.bar, foobar, bar, bar.foo and baroo .
  • Q(module_endswith='bar' will match events from foo.bar and foobar.
  • Q(module_contains='ip' will match events from lipsum.
  • Q(module_in=['foo', 'bar'] will match events from foo and bar.
  • Q(module_regex=r"(re|sre.*)\b") will match events from ``re, re.foobar, srefoobar but not from repr.

• Removed the merge option. Now when you call hunter.trace(...) multiple times only the last one is active. BACKWARDS INCOMPATIBLE

• Remove the previous_tracer handling. Now when you call hunter.trace(...) the previous tracer (whatever was in sys.gettrace()) is disabled and restored when hunter.stop() is called. BACKWARDS INCOMPATIBLE

• Fixed CodePrinter to show module name if it fails to get any sources.

0.6.0 (2015-10-10)

• Added a clear_env_var option on the tracer (disables tracing in subprocess).
• Added force_colors option on hunter.actions.VarsPrinter and hunter.actions.CodePrinter.
• Allowed setting the stream to a file name (option on hunter.actions.VarsPrinter and hunter.actions.CodePrinter).
• Bumped up the filename alignment to 40 cols.
• If not merging then self is not kept as a previous tracer anymore. Closes #16.
• Fixed handling in VarsPrinter: properly print eval errors and don’t try to show anything if there’s an AttributeError. Closes #18.
• Added a stdlib boolean flag (for filtering purposes). Closes #15.
• Fixed broken frames that have “None” for filename or module (so they can still be treated as strings).
• Corrected output files in the install_lib command so that pip can uninstall the pth file. This only works when it’s installed with pip (sadly, setup.py install/develop and pip install -e will still leave pth garbage on pip uninstall hunter).

0.5.1 (2015-04-15)

• Fixed hunter.event.Event.globals to actually be the dict of global vars (it was just the locals).

0.5.0 (2015-04-06)

• Fixed hunter.And() and hunter.Or() “single argument unwrapping”.
• Implemented predicate compression. Example: Or(Or(a, b), c) is converted to Or(a, b, c).
• Renamed hunter.event.Event.source to hunter.event.Event.fullsource.
• Added hunter.event.Event.source that doesn’t do any fancy sourcecode tokenization.
• Fixed hunter.event.Event.fullsource return value for situations where the tokenizer would fail.
• Made the print function available in the PYTHONHUNTER env var payload.
• Added a __repr__ for hunter.event.Event.

0.4.0 (2015-03-29)

• Disabled colors for Jython. Contributed by Claudiu Popa in #12.
• Test suite fixes for Windows. Contributed by Claudiu Popa in #11.
• Added an introduction section in the docs.
• Implemented a prettier fallback for when no sources are available for that frame.
• Implemented fixups in cases where you use action classes as a predicates.

0.3.1 (2015-03-29)

• Forgot to merge some commits …

0.3.0 (2015-03-29)

• Added handling for internal repr failures.
• Fixed issues with displaying code that has non-ascii characters.
• Implemented better display for call frames so that when a function has decorators the function definition is shown (instead of just the first decorator). See: #8.

0.2.1 (2015-03-28)

• Added missing color entry for exception events.
• Added hunter.event.Event.line property. It returns the source code for the line being run.

0.2.0 (2015-03-27)

• Added color support (and colorama as dependency).
• Added support for expressions in hunter.actions.VarsPrinter.
• Breaking changes:
  • Renamed F to hunter.Q(). And hunter.Q() is now just a convenience wrapper for hunter.predicates.Query.
  • Renamed the PYTHON_HUNTER env variable to PYTHONHUNTER.
  • Changed hunter.predicates.When to take positional arguments.
  • Changed output to show 2 path components (still not configurable).
  • Changed hunter.actions.VarsPrinter to take positional arguments for the names.
• Improved error reporting for env variable activation (PYTHONHUNTER).
• Fixed env var activator (the .pth file) installation with setup.py install (the “egg installs”) and setup.py develop/pip install -e (the “egg links”).

0.1.0 (2015-03-22)

• First release on PyPI.

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