How can I use valgrind with Python C++ extensions?

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Question :

How can I use valgrind with Python C++ extensions?

I have Python extensions implemented on C++ classes. I don’t have a C++ target to run valgrind with. I want to use valgrind for memory check.

Can I use valgrind with Python?

Asked By: neuron

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Answer #1:

Yes, you can use valgrind with Python. You just need to use the valgrind suppression file provided by the Python developers, so you don’t get a bunch of false positives due to Python’s custom memory allocation/reallocation functions.

The valgrind suppression file can be found here: http://svn.python.org/projects/python/trunk/Misc/valgrind-python.supp

IMPORTANT: You need to uncomment the lines for PyObject_Free and PyObject_Realloc in the suppression file*.

The recommended usage syntax is:

$ valgrind --tool=memcheck --suppressions=valgrind-python.supp 
                                          python -E -tt ./my_python_script.py

See also this README file from the Python SVN repo which describes the different ways of using Python with valgrind:
http://svn.python.org/projects/python/trunk/Misc/README.valgrind

* – Alternatively, you can recompile Python with PyMalloc disabled, which allows you to catch more memory leaks that won’t show up if you just suppress PyMalloc.

Answered By: Steven T. Snyder

Answer #2:

In Python 2.7 and 3.2 there is now a --with-valgrind compile-time flag that allows the Python interpreter to detect when it runs under valgrind and disables PyMalloc. This should allow you to more accurately monitor your memory allocations than otherwise, as PyMalloc just allocates memory in big chunks.

Answered By: Kamil Kisiel

Answer #3:

Yes you can: you do have a target to run valgrind with — it’s the python interpreter itself:

valgrind python foo.py

However, the results of above may not be very satisfactory — Python is built in opt mode and with a special malloc, which may drown you in false positives.

You’ll likely get better results by first building a debug version of Python. Start here.

Answered By: Employed Russian

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