"py.test" vs "pytest" command

The py.test command is failing in my case, whereas pytest is running totally fine.

I use the pytest-flask plugin:

platform linux -- Python 3.5.2, pytest-3.0.2, py-1.4.31, pluggy-0.3.1
rootdir: /home/sebastian/develop/py/flask-rest-template, inifile: 
plugins: flask-0.10.0

When I invoke $ py.test I get the following error:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 301, in _getconftestmodules
    return self._path2confmods[path]
KeyError: local('/home/sebastian/develop/py/flask-rest-template')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 332, in _importconftest
    return self._conftestpath2mod[conftestpath]
KeyError: local('/home/sebastian/develop/py/flask-rest-template/conftest.py')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/_pytest/config.py", line 338, in _importconftest
    mod = conftestpath.pyimport()
  File "/usr/local/lib/python3.5/dist-packages/py/_path/local.py", line 650, in pyimport
    __import__(modname)
  File "/usr/local/lib/python3.5/dist-packages/_pytest/assertion/rewrite.py", line 207, in load_module
    py.builtin.exec_(co, mod.__dict__)
  File "/home/sebastian/develop/py/flask-rest-template/conftest.py", line 2, in <module>
    from app.app import create_app
  File "/home/sebastian/develop/py/flask-rest-template/app/app.py", line 1, in <module>
    from flask import Flask
ImportError: No module named 'flask'
ERROR: could not load /home/sebastian/develop/py/flask-rest-template/conftest.py

This is my actual conftest.py file:

import pytest
from app.app import create_app

@pytest.fixture
def app():
    app = create_app()
    return app

My project structure is as like:

.
├── app
│   ├── __init__.py
│   ├── app.py
│   └── config.py   # flask configuration objects
├── conftest.py     # pytest configruation
├── requirements.txt
├── ...
└── tests
    └── ...

So, what is the difference between the two commands? And why is one failing and the other not?

---

update 1

1) I had to change my relative imports from .config import Config or from config import Config to absolute ones like from app.config import Config

2) Running flask with python3 -m app.app

3) now pytest and py.test work normal

Thank you very much for your help, folks!

---

update 2

This is getting weird… when using absolute imports, running python with the -m option and flask with debug=True then the werkzeug library is not reloading the sources as expected:

http://chase-seibert.github.io/blog/2015/06/12/flask-werkzeug-reloader-python-dash-m.html

https://github.com/pallets/werkzeug/issues/461

https://github.com/pallets/flask/issues/1246

This helped me in my app/app.py:

if __name__ == '__main__':
    app.run(debug=True, use_reloader=False)

Then python -m app.app works fine.