pytest cannot import module while python can

Question

I am working on a package in Python. I use virtualenv. I set the path to the root of the module in a .pth path in my virtualenv, so that I can import modules of the package while developing the code and do testing (Question 1: is it a good way to do?). This works fine (here is an example, this is the behavior I want):

(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ python
Python 2.7.12 (default, Jul  1 2016, 15:12:24) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from rc import ns
>>> exit()
(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ python tests/test_ns.py 
issued command: echo hello
command output: hello

However, if I try to use PyTest, I get some import error messages:

(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ pytest
=========================================== test session starts ============================================
platform linux2 -- Python 2.7.12, pytest-3.0.5, py-1.4.31, pluggy-0.4.0
rootdir: /home/zz/Desktop/GitFolders/rc, inifile: 
collected 0 items / 1 errors 

================================================== ERRORS ==================================================
________________________________ ERROR collecting tests/test_ns.py ________________________________
ImportError while importing test module '/home/zz/Desktop/GitFolders/rc/tests/test_ns.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_ns.py:2: in <module>
    from rc import ns
E   ImportError: cannot import name ns
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
========================================= 1 error in 0.09 seconds ==========================================
(VEnvTestRc) zz@zz:~/Desktop/GitFolders/rc$ which pytest
/home/zz/Desktop/VirtualEnvs/VEnvTestRc/bin/pytest

I am a bit puzzled, it looks like this indicates an import error, but Python does it fine so why is there a problem specifically with PyTest? Any suggestion to the reason / remedy (Question 2)? I googled and stack-overflowed the 'ImportError: cannot import' error for PyTest, but the hits I got were related to missing python path and remedy to this, which does not seem to be the problem here. Any suggestions?

Answer 1

[Resolved] Before directly jumping into the solution of removing/ adding __init__.py, we might also want to look at how the imports are been done in your classes. Actually, I lost a day playing around with just __init__.py thinking that might be the problem :) However, that was quite informative.

In my case, it was the wrong way of calling classes from one python class to another python class which was throwing ImportError. Fixed the way classes/ modules to be called and it worked like charm. Hope, this helps others as well.

And yes, for similar error, we might have different solutions depending on how the code is written. Better to spend more time on self debugging. Lesson Learnt :) Happy coding!!!

Answer 2

For anyone who tried everything and still getting error,I have a work around.

In the folder where pytest is installed,go to pytest-env folder.

Open pyvenv.cfg file.

In the file change include-system-site-packages from false to true.

home = /usr/bin
include-system-site-packages = true
version = 3.6.6

Hope it works .Don't forget to up vote.

Answer 3

I had the same problem but for another reason than the ones mentioned:

I had py.test installed globally, while the packages were installed in a virtual environment.

The solution was to install pytest in the virtual environment. (In case your shell hashes executables, as Bash does, use hash -r, or use the full path to py.test)

Answer 4

It could be that Pytest is not reading the package as a Python module while Python is (likely due to path issues). Try changing the directory of the pytest script or adding the module explicitly to your PYTHONPATH.

Or it could be that you have two versions of Python installed on your machine. Check your Python source for pytest and for the python shell that you run. If they are different (i.e. Python 2 vs 3), use source activate to make sure that you are running the pytest installed for the same python that the module is installed in.

Answer 5

If you already have .pyc files, try to delete them.

Today, I encounter this problem, here is what happend:

first I run pytest in mac (this will generate pyc files) then I launch a docker container (the os is alpine), with project dir mounted, and then when I try to run pytest in container, ImportError happens. after cleaning all pyc files, no error any more.

Hope this may be helpful.