Add support for valgrind's memcheck feature

[vbraun]

Also tox & some simple tests

[tekknolagi]

Hi @vbraun thanks for the contribution! I will merge probably when I get home from my work trip. I have a few broader comments that you can either address before then or I will tackle after:

• Please don't add new dependencies; unittest should be enough here
• Please write callgrind files to a tempfile (using TemporaryFile or TemporaryDirectory) in tests; then you don't need any cleanup or gitignore
• Should the supp file be part of the test directory? Does it need to be used in normal operation? I've never had luck running memcheck against CPython.
• Related, how likely is the supp file to become out of date?

[vbraun]

Just python -m unittest isn't enough, since the tests need to run in a Python instance that runs inside valgrind. Options are basically:

• You need to remember all the valgrind command line options, good luck (and different tests need different valgrind options)
• The tests could run valgind (and then a second python instance) as subprocess (Inception)
• Or there could be a shell script to run valgind python unittest with the right parameters.
• Or (thats the route I took) use tox which has custom test commands. Tox is also nice in that multiple python versions can be tested easily.

Either way is feasible, let me know which you prefer.

Related, the output file is a bit tricky:

• The callgrind output file has to be specified on the valgrind commandline
• valgrind executes Python
• Python runs tests

So you can't just use TemporaryDirectory. Depending on how you want to launch valgind -> python -> unittest, the directory needs to be chosen first and then passed down to the test.

The suppression file changes rather slowly with CPython versions, but it does. You also need to take the one from the CPython repo and then make edits by hand (as indicated in comments), so you can't just download it. It is also incomplete, with different false positives for different Python versions :-/ . Here again tox is kind of nice since you can at least compare output for different versions easily.