DeprecationWarning when used with pytest

[cubranic]

Describe the bug
Using pyfakefs with pytest produces a deprecation warning about the compiler package as soon as a test depends on the fs fixture.

plugins: pyfakefs-3.5.6
collected 1 item

tests/test_foo.py .                                                                                           [100%]

================================================= warnings summary ==================================================
tests/test_foo.py::test_fs
  /usr/local/miniconda3/envs/alpenhorn/lib/python2.7/site-packages/py/_code/_assertionold.py:3: DeprecationWarning: The compiler package is deprecated and removed in Python 3.x.
    from compiler import parse, ast, pycodegen

-- Docs: https://docs.pytest.org/en/latest/warnings.html
======================================= 1 passed, 1 warnings in 0.11 seconds ========================================

How To Reproduce
Put the following into test_foo.py:

def test_foo(fs):
    pass

Then run pytest test_foo.py.

Your enviroment
Please run the following and paste the output.

Darwin-18.0.0-x86_64-i386-64bit
('Python', '2.7.15 |Anaconda, Inc.| (default, Dec 14 2018, 13:10:39) \n[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)]')
('pyfakefs', '3.5.6')

[mrbean-bremen]

There is an old (and long fixed) pytest bug, which may be related - can you please check which version of pytest you use?

[cubranic]

Showing DeprecationWarnings from system libraries has been enabled in Pytest 3.8. I'm running Pytest 4.1.1, the latest version on Conda.

[cubranic]

I was able to silence the warning with a filter in the configuration file, as described on the same Pytest page. But if pytest is directly importing the compiler package, perhaps the import statement can be wrapped in some kind of logging filter?

[mrbean-bremen]

Ah, ok - I had used an older version of pytest, now I see the warning, too, thanks!
It is strange that this warning is still occurring (pytest is imported a lot if used in tests), but wrapping the import in a logging filter sounds like a good idea.

[mrbean-bremen]

Hm, I didn't succeed in filtering out the warning so far (other than in the config file or on the command line) - maybe I'm doing something wrong. I will check again another day.

[mrbean-bremen]

I had another try, and couldn't get it to work - either I'm doing something wrong, or this has to be fixed in pytest itself. I'm out of ideas right now. @jmcgeheeiv - any thoughts?

[diefans]

@mrbean-bremen

[pytest]
filterwarnings =
    ignore::DeprecationWarning 

# pyfakefs/fake_filesystem_unittest.py
# line 482
            with warnings.catch_warnings():
                warnings.simplefilter("ignore")
                modules = {name: mod for name, mod in module.__dict__.items()
                           if is_fs_module(mod, name)}

[mrbean-bremen]

@diefans - thanks! I will have a look at this sometime next week, I'm traveling right now.

[jmcgeheeiv]

I'm sorry, but I do not see what the problem could be.

[diefans]

When I put catch_warnings context around modules = ... I do not get deprecation warnings in python 2.7...

[mrbean-bremen]

@diefans - thanks for that - this works nicely! I obviously had put the filter into the wrong place.
And we can make this very specific to suppress only this one warning...