`py.test` and `__init__.py` files

Question

I thought py.test is "standalone" in a sense that it treats test_*.py files "as it is", and only imports modules specified in these files, with no respect to any surrounding files. It looks like I'm wrong. Here is my dialog with py.test:

$ ls
__init__.py    test_pytest.py
$ cat __init__.py 
$ cat test_pytest.py 
def test_pytest():
    assert True
$ py.test test_pytest.py 
========================================================= test session starts ==========================================================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 0 items / 1 errors 

================================================================ ERRORS ================================================================
___________________________________________________ ERROR collecting test_pytest.py ____________________________________________________
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/py-1.4.5-py2.7.egg/py/_path/local.py:529: in pyimport
>           mod = __import__(modname, None, None, ['__doc__'])
E           ImportError: No module named test_pytest
======================================================= 1 error in 0.01 seconds ========================================================
$ rm __init__.py 
$ py.test test_pytest.py 
========================================================= test session starts ==========================================================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 1 items 

test_pytest.py .

======================================================= 1 passed in 0.01 seconds =======================================================
$ 

How do I make py.test work and still have my __init__.py files?

UPDATE

In comments, Holger Krekel asked, what is the name of parent directory. And it turns out that I can reproduce the error above only having a certain parent directory name (e.g. the same name as one of the packages installed, like distutils). See here:

~/test_min 
$ tree
.
└── distutils
    ├── __init__.py
    └── test_pytest.py

1 directory, 2 files
~/test_min 
$ cat distutils/__init__.py 
~/test_min 
$ cat distutils/test_pytest.py 
def test_pytest():
    assert True
~/test_min 
$ py.test distutils/test_pytest.py 
======================== test session starts =========================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 0 items / 1 errors 

=============================== ERRORS ===============================
_____________ ERROR collecting distutils/test_pytest.py ______________
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/py-1.4.5-py2.7.egg/py/_path/local.py:529: in pyimport
>           mod = __import__(modname, None, None, ['__doc__'])
E           ImportError: No module named test_pytest
====================== 1 error in 0.01 seconds =======================
~/test_min 
$ rm distutils/__init__.py 
~/test_min 
$ py.test distutils/test_pytest.py 
======================== test session starts =========================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 1 items 

distutils/test_pytest.py .

====================== 1 passed in 0.01 seconds ======================
~/test_min 
$ touch __init__.py
~/test_min 
$ ls
__init__.py distutils
~/test_min 
$ touch distutils/__init__.py
~/test_min 
$ py.test distutils/test_pytest.py 
======================== test session starts =========================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 1 items 

distutils/test_pytest.py .

====================== 1 passed in 0.02 seconds ======================
~/test_min 
$ rm __init__.py 
~/test_min 
$ py.test distutils/test_pytest.py 
======================== test session starts =========================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 0 items / 1 errors 

=============================== ERRORS ===============================
_____________ ERROR collecting distutils/test_pytest.py ______________
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/py-1.4.5-py2.7.egg/py/_path/local.py:529: in pyimport
>           mod = __import__(modname, None, None, ['__doc__'])
E           ImportError: No module named test_pytest
====================== 1 error in 0.01 seconds =======================
~/test_min 
$ mv distutils foobar
~/test_min 
$ py.test foobar/test_pytest.py 
======================== test session starts =========================
platform darwin -- Python 2.7.2 -- pytest-2.1.3
collected 1 items 

foobar/test_pytest.py .

====================== 1 passed in 0.01 seconds ======================
~/test_min 
$ 

Hope this additional information will help.

Answer 1

Looks like py.test is using py._path.pyimport to open your file. If there is a __init__.py file in the directory, it treats your file as a module, otherwise it opens the file. Long story short, delete the __init__.py or put your tests in another directory outside your project code (<--- good idea).

https://py.readthedocs.io/en/latest/path.html#py._path.local.LocalPath.pyimport

Answer 2

I really suggest you to rename the directory to something not called "distutils". Why ? Because you are overriding an existing module. When "import distutils" or "from distutils import *" appear in the script (from another import or your own python file), it will prefer your directory instead the system one. If the module distutils have been already loaded before, your distutils will not be loaded, because the symbol already exists in global().

It would be really simpler to rename that directory (like tests) instead of trying to fight with py.text / python internals.