Question about Importing Modules under Pytest

I have been converting some tests written earlier for Unittest and am having trouble with import statements when running them with Pytest.

As an example, in the older code the module create.py in directory lib might be imported as

import lib.create

but this syntax usually raises errors when I run the code with Pytest.

Solution found: see below.

---

I'd appreciate any advice. I've placed a minimal example in the files in this repository. After cloning, enter the set up under Python 2.7 with:

cd pytest_import_question
virtualenv v_env27
. v_env27/bin/activate
pip install -Ur requirements.txt
py.test tests

Running Pytest from within pytest_import_question typically generates an ImportError:

$ py.test tests
============================= test session starts ==============================
platform darwin -- Python 2.7.6 -- py-1.4.26 -- pytest-2.7.0
rootdir: .../pytest_import_question/tests, inifile:
collected 0 items / 1 errors

==================================== ERRORS ====================================
_______________________ ERROR collecting test_caller.py ________________________
tests/test_caller.py:3: in <module>
    import lib.create
E   ImportError: No module named lib.create
=========================== 1 error in 0.01 seconds ============================

Other comments:

1. Directory structure is as follows:

   pytest_import_question/
       lib/
           __init__.py
           create.py
       tests/
           test_caller.py

2. File __init__.py is empty. The other two files are a test file that calls lib/create.py:

   # test_caller.py
   
   import lib.create
   
   def test_show():
       assert True

   and lib/create.py itself, which contains a minimal function:

   # create.py
   
   def create():
       pass

3. I have tried updating the sys.path list in test_caller.py:

   import sys
   sys.path.append('lib')

   or

   import sys
   sys.path.extend(['..', 'lib'])

   but the result is the same.

4. The example works with nose, however:

   $ nosetests tests/
   .
   ----------------------------------------------------------------------
   Ran 1 test in 0.003s

   Why not with Pytest? Is there a workaround?

---

Thanks for any suggestions as to how to deal with this.

Solution

The solution is include a setup.py file at the top-level directory of the project, and then to use pip to install it in "editable mode"

pip install -e .

That will generate a directory whose name ends in .egg-info and which contains a number of configuration files. After that, running with Pytest takes place without difficulties.

[end]