hunter 2.2.0

Hunter is a flexible code tracing toolkit.

========
Overview
========



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 <https://python-hunter.readthedocs.io/en/latest/introduction.html>`_,
a `convenient terminal API <environment-variable-activation>`_ and
a `CLI tool to attach to processes <tracing-processes>`_.

* Free software: BSD 2-Clause License

Installation
============

::

pip install hunter

Documentation
=============


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

Overview
========

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

.. sourcecode:: python

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

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

That would result in:

.. sourcecode:: pycon

>>> os.path.join('a', 'b')
/usr/lib/python3.5/posixpath.py:71 call => join(a='a')
/usr/lib/python3.5/posixpath.py:76 line sep = _get_sep(a)
/usr/lib/python3.5/posixpath.py:39 call => _get_sep(path='a')
/usr/lib/python3.5/posixpath.py:40 line if isinstance(path, bytes):
/usr/lib/python3.5/posixpath.py:43 line return '/'
/usr/lib/python3.5/posixpath.py:43 return <= _get_sep: '/'
/usr/lib/python3.5/posixpath.py:77 line path = a
/usr/lib/python3.5/posixpath.py:78 line try:
/usr/lib/python3.5/posixpath.py:79 line if not p:
/usr/lib/python3.5/posixpath.py:81 line for b in p:
/usr/lib/python3.5/posixpath.py:82 line if b.startswith(sep):
/usr/lib/python3.5/posixpath.py:84 line elif not path or path.endswith(sep):
/usr/lib/python3.5/posixpath.py:87 line path += sep + b
/usr/lib/python3.5/posixpath.py:81 line for b in p:
/usr/lib/python3.5/posixpath.py:91 line return path
/usr/lib/python3.5/posixpath.py:91 return <= join: 'a/b'
'a/b'

In a terminal it would look like:

.. image:: https://raw.githubusercontent.com/ionelmc/python-hunter/master/docs/code-trace.png


Custom 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). Example:

.. sourcecode:: python

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

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

That would result in:

.. sourcecode:: pycon

>>> os.path.join('a', 'b')
/usr/lib/python3.5/posixpath.py:71 call def join(a, *p):
/usr/lib/python3.5/posixpath.py:76 line sep = _get_sep(a)
/usr/lib/python3.5/posixpath.py:39 call def _get_sep(path):
/usr/lib/python3.5/posixpath.py:40 line if isinstance(path, bytes):
/usr/lib/python3.5/posixpath.py:43 line return '/'
/usr/lib/python3.5/posixpath.py:43 return return '/'
... return value: '/'
/usr/lib/python3.5/posixpath.py:77 line path = a
/usr/lib/python3.5/posixpath.py:78 line try:
/usr/lib/python3.5/posixpath.py:79 line if not p:
/usr/lib/python3.5/posixpath.py:81 line for b in p:
/usr/lib/python3.5/posixpath.py:82 line if b.startswith(sep):
/usr/lib/python3.5/posixpath.py:84 line elif not path or path.endswith(sep):
/usr/lib/python3.5/posixpath.py:87 line path += sep + b
/usr/lib/python3.5/posixpath.py:81 line for b in p:
/usr/lib/python3.5/posixpath.py:91 line return path
/usr/lib/python3.5/posixpath.py:91 return return path
... return value: 'a/b'
'a/b'

- or in a terminal:

.. image:: https://raw.githubusercontent.com/ionelmc/python-hunter/master/docs/simple-trace.png

------

Another useful action is the ``VarsPrinter``:

.. sourcecode:: python

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:

.. sourcecode:: pycon

>>> os.path.join('a', 'b')
/usr/lib/python3.5/posixpath.py:71 call def join(a, *p):
/usr/lib/python3.5/posixpath.py:76 line sep = _get_sep(a)
vars path => 'a'
/usr/lib/python3.5/posixpath.py:39 call def _get_sep(path):
vars path => 'a'
/usr/lib/python3.5/posixpath.py:40 line if isinstance(path, bytes):
vars path => 'a'
/usr/lib/python3.5/posixpath.py:43 line return '/'
vars path => 'a'
/usr/lib/python3.5/posixpath.py:43 return return '/'
... return value: '/'
/usr/lib/python3.5/posixpath.py:77 line path = a
vars path => 'a'
/usr/lib/python3.5/posixpath.py:78 line try:
vars path => 'a'
/usr/lib/python3.5/posixpath.py:79 line if not p:
vars path => 'a'
/usr/lib/python3.5/posixpath.py:81 line for b in p:
vars path => 'a'
/usr/lib/python3.5/posixpath.py:82 line if b.startswith(sep):
vars path => 'a'
/usr/lib/python3.5/posixpath.py:84 line elif not path or path.endswith(sep):
vars path => 'a'
/usr/lib/python3.5/posixpath.py:87 line path += sep + b
vars path => 'a/b'
/usr/lib/python3.5/posixpath.py:81 line for b in p:
vars path => 'a/b'
/usr/lib/python3.5/posixpath.py:91 line return path
vars path => 'a/b'
/usr/lib/python3.5/posixpath.py:91 return return path
... return value: 'a/b'
'a/b'

In a terminal it would look like:

.. image:: https://raw.githubusercontent.com/ionelmc/python-hunter/master/docs/vars-trace.png

-----

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):

.. sourcecode:: python

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:

.. sourcecode:: python

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:

.. sourcecode:: pycon

>>> 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:

.. image:: https://raw.githubusercontent.com/ionelmc/python-hunter/master/docs/tree-trace.png

.. _tracing-processes:

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 ``pip install 'hunter[remote]'`` and 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 <https://python-hunter.readthedocs.org/en/latest/remote.html>`_.

**Note:** Windows ain't supported.

.. _environment-variable-activation:

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_sw='django')"
PYTHONHUNTER="Q(module_sw='celery')"

which is the equivalent of::

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

which is the equivalent of::

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



Filtering DSL
-------------

Hunter supports a flexible query DSL, see the `introduction
<https://python-hunter.readthedocs.org/en/latest/introduction.html>`_.

Development
===========

To run the all tests run::

tox


FAQ
===

Why not Smiley?
---------------

There's some obvious overlap with `smiley <https://pypi.python.org/pypi/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 <https://pypi.python.org/pypi/pytrace>`_ is another tracer tool. It seems quite similar to Smiley - it uses a sqlite
database for the events, threads and IPC.

TODO: Expand this.

Why (not) coverage?
-------------------

For purposes of debugging `coverage <https://pypi.python.org/pypi/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.


Changelog
=========

2.2.0 (2019-01-19)
------------------

* Added ``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 <https://pypi.org/project/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 <https://python-fields.readthedocs.io/en/stable/>`_.
* 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 ``CallPrinter`` action (shoudln'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 ``Event.count`` and ``Event.calls`` attributes.
* Added the ``lt``/``lte``/``gt``/``gte`` lookups.
* Added convenience aliases for ``startswith`` (``sw``), ``endswith`` (``ew``) and ``regex`` (``rx``).
* Added a convenience ``hunter.wrap`` decorator to start tracing around a function.
* Added support for remote tracing (with two backends: `manhole <https://pypi.python.org/pypi/manhole>`__ and GDB) via
the ``hunter-trace`` bin. Note: **Windows is NOT SUPPORTED**.
* Changed the default action to ``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 <https://github.com/ionelmc/python-hunter/issues/30>`_). A
`# cython: linetrace=True` stanza or equivalent is required in Cython modules for this to work.

1.3.0 (2016-04-14)
------------------

* Added ``Event.thread``.
* Added ``Event.threadid`` and ``Event.threadname`` (available for filtering with ``Q`` objects).
* Added ``threading_support`` argument to ``hunter.trace``: makes new threads be traced and changes action output to include
threadname.
* Added support for using `pdb++ <https://pypi.python.org/pypi/pdbpp>`_ in the ``Debugger`` action.
* Added support for using `manhole <https://pypi.python.org/pypi/manhole>`_ via a new ``Manhole`` action.
* Made the ``handler`` a public but readonly property of ``Tracer`` objects.


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 ``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 ``VarsPrinter``'s initializer.
* Added a ``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 <https://github.com/ionelmc/python-hunter/issues/23>`_.
* Fixed ``stdlib`` checks (wasn't very reliable). Closes `#24 <https://github.com/ionelmc/python-hunter/issues/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 ``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 <https://github.com/ionelmc/python-hunter/issues/16>`_.
* Fixed handling in VarsPrinter: properly print eval errors and don't try to show anything if there's an AttributeError.
Closes `#18 <https://github.com/ionelmc/python-hunter/issues/18>`_.
* Added a ``stdlib`` boolean flag (for filtering purposes).
Closes `#15 <https://github.com/ionelmc/python-hunter/issues/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 ``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 <https://github.com/ionelmc/python-hunter/pull/12>`_).
* Test suite fixes for Windows (contributed by Claudiu Popa in `#11 <https://github.com/ionelmc/python-hunter/pull/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 <https://github.com/ionelmc/python-hunter/issues/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 ``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.