hunter 3.3.3

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="".

PYTHONHUNTERCONFIG="stdlib=False,force_colors=True"

Filtering DSL

Hunter supports a flexible query DSL, see the introduction.

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.

3.3.3 (2021-05-04)

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

  Python unfortunatelly only allows removing the trace function for the current thread - now hunter.tracer.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 hunter.actions.StackPrinter action.

• Implemented the hunter.predicates.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 hunter.predicates.Backlog.

• Implemented the hunter.actions.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 hunter.actions.ErrorSnooper - an action that detects silenced exceptions.

• Added hunter.load_config and fixed issues with configuration being loaded too late from the PYTHONHUNTERCONFIG environment variable.

• Changed hunter.From helper to automatically move depth and calls filters to the predicate (so they filter after hunter.predicates.From activates).

• Changed hunter.predicates.From to pass a copy of event to the predicate. The copy will have the depth and calls attributes adjusted to the point where hunter.predicates.From activated.

• Fixed a bunch of inconsistencies and bugs when using & and | operators with predicates.

• Fixed a bunch of broken fields on detached events <hunter.event.Event.detach> (hunter.event.Event.function_object and hunter.event.Event.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: hunter.actions.ColorStreamAction.

• Fixed __repr__ for the hunter.predicates.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: hunter.actions.ColorStreamAction.

3.0.2 (2019-10-10)

• Fixed setting stream from PYTHONHUNTERCONFIG environment variable. See: hunter.actions.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 hunter.actions.ColorStreamAction.filename_prefix, hunter.actions.ColorStreamAction.output, hunter.actions.ColorStreamAction.pid_prefix, hunter.actions.ColorStreamAction.thread_prefix, hunter.actions.ColorStreamAction.try_repr and hunter.actions.ColorStreamAction.try_source methods to the hunter.actions.ColorStreamAction baseclass.

• Added hunter.actions.VarsSnooper - a PySnooper-inspired variant of hunter.actions.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.