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Hunter is a flexible code tracing toolkit.

Project description

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 and a convenient terminal API (see Environment variable activation).

  • Free software: BSD license


pip install hunter



The default action is to just print the code being executed. Example:

import hunter

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

Would result in:

python2.7/    call      def join(a, *p):
python2.7/    line          path = a
python2.7/    line          for b in p:
python2.7/    line              if b.startswith('/'):
python2.7/    line              elif path == '' or path.endswith('/'):
python2.7/    line                  path += '/' + b
python2.7/    line          for b in p:
python2.7/    line          return path
python2.7/    return        return path
                             ...       return value: 'a/b'
  • or in a terminal:

You can have custom actions, like a variable printer - example:

import hunter
hunter.trace(hunter.Q(module='posixpath', action=hunter.VarsPrinter('path')))

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

Would result in:

python2.7/    call      def join(a, *p):
python2.7/    line          path = a
                             vars      path => 'a'
python2.7/    line          for b in p:
                             vars      path => 'a'
python2.7/    line              if b.startswith('/'):
                             vars      path => 'a'
python2.7/    line              elif path == '' or path.endswith('/'):
                             vars      path => 'a'
python2.7/    line                  path += '/' + b
                             vars      path => 'a/b'
python2.7/    line          for b in p:
                             vars      path => 'a/b'
python2.7/    line          return path
                             vars      path => 'a/b'
python2.7/    return        return path
                             ...       return value: 'a/b'
  • or in a terminal:

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):

TODO: More examples.

Environment variable activation

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

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

On Windows you’d do something like:

set PYTHONHUNTER=module='os.path'

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 *

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

Filtering DSL

Hunter supports a flexible query DSL, see the introduction.


To run the all tests run:



Why not Smiley?

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

  • Complexity. Smiley is simply over-engineered:

    • It’s 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 might way 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) 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.


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, and foobar.

    • Q(module_startswith=['foo', 'bar'] will match events from foo,, foobar, bar, and baroo .

    • Q(module_endswith='bar' will match events from 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 VarsPrinter and CodePrinter.

  • Allowed setting the stream to a file name (option on VarsPrinter and 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, install/develop and pip install -e will still leave pth garbage on pip uninstall hunter).

0.5.1 (2015-04-15)

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

0.5.0 (2015-04-06)

  • Fixed And and Or “single argument unwrapping”.

  • Implemented predicate compression. Example: Or(Or(a, b), c) is converted to Or(a, b, c).

  • Renamed the Event.source to Event.fullsource.

  • Added Event.source that doesn’t do any fancy sourcecode tokenization.

  • Fixed 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 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 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 VarsPrinter.

  • Breaking changes:

    • Renamed F to Q. And Q is now just a convenience wrapper for Query.

    • Renamed the PYTHON_HUNTER env variable to PYTHONHUNTER.

    • Changed When to take positional arguments.

    • Changed output to show 2 path components (still not configurable).

    • Changed 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 install (the “egg installs”) and develop/pip install -e (the “egg links”).

0.1.0 (2015-03-22)

  • First release on PyPI.

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