isfile check fails within pytest

[satra]

the test below fails when running with pytest test.py but not with pytest -s test.py

• pip list of the virtual environment you are using

$ pip list
pip (8.1.2)
py (1.4.31)
pytest (3.0.3)
setuptools (27.2.0)
wheel (0.29.0)

• pytest and operating system versions

python 3.5.2
pytest 3.0.3
OS X (but i believe this fails on other OSes as well)

• Minimal example if possible

import os

def test_isfile():
    assert os.path.isfile(True) == False

[nicoddemus]

Oh wow, that's strange. Thanks for the report!

[nicoddemus]

It also passes with pytest test.py --capture=sys, so definitely has to do with file-descriptor capturing.

[nicoddemus]

I think it's related to the fact that capfd is redirecting file descriptor 1 to a file, and 1 equals True. The same test fails if we pass 1 or 2 instead of True (equivalent to stdout and stderr), but not integers higher than that.

[The-Compiler]

I don't think this is a bug. The same code (which simply tests if stdout is a file, in a rather obfuscated way) also fails without pytest involved when doing python foo.py > file.

[satra]

@The-Compiler - you are correct in that python 3 treats 1 and True identically even though they have different datatypes. on python 2 this raises a TypeError.

would the recommendation for this test be to do: with capfd.disabled(): ? we will also look to see if we can modify the upstream code that this is testing.

[The-Compiler]

bool is a subclass of int (isinstance(True, int) == True) both on Python 2 and Python 3. The reason this doesn't work on Python 2 is that os.path.isfile only accept paths (and not ints as file descriptors) there.

What's the point of this test, or how is the actual test looking like? At least with your minimal example, I think the test should just not exist at all 😉

[satra]

essentially it's an embedded test of hashing a hierarchical dictionary. the key value pairs could have as value a file path. and the os.path.isfile(value) checks to see if it's a file and replaces the value with content hash of the file. since some of the values are True bools the test started failing with pytest, when it didn't fail with nose.

[nicoddemus]

I would recommend using capfd.disabled() in this case if it solves this specific problem. IMO this is a very edge-case and not much can be done on our side to fix this. Feel free to reopen if you feel otherwise and this warrants more discussion.