pytest running with another version of python

Question

I've installed pyenv and have different versions of python installed with it:

$ pyenv versions
  system
  2.7.1
  3.2.5
  3.5.0
  3.5.1
* 3.5.2

I use the following command to switch to python 3.5.2:

pyenv shell 3.5.2

And when I check the python version this is what I get:

$ python --version
Python 3.5.2

But when I run pytest, it still runs under python 2.7.6:

pytest -v
==================================================================== test session starts ====================================================================
platform linux2 -- Python 2.7.6, pytest-3.0.3, py-1.4.31, pluggy-0.4.0 -- /usr/bin/python

Why is pytest running under the older version?

What do `which python` and `which pytest` show? Are the pointed-to files links or some launcher scripts? You may also try `hash -r` to eliminate the case of stale `bash` path cache. — ivan_pozdeev, Nov 21 '16 at 11:38
@ivan_pozdeev `which python` => `/home/meysam/.pyenv/shims/python` - `which pytest` => `/usr/local/bin/pytest` — B Faley, Nov 21 '16 at 12:20
From the `which` out you learn that `python` uses the python version in your environment, however `pytest` uses the globally available one, that is located under `/usr/local/...`. To run Pytest inside your virtual environment, first install it using `python -m pip install pytest` and then run `python -m pytest`. — RealA10N, Sep 15 '21 at 16:46

score 35 · Accepted Answer · edited May 23 '17 at 12:00

Bottom line: run

python -m pytest, or
py.test-<version> if your alternative Python and pytest are installed with system package manager, or
if your alternative Python has been installed with pyenv, switch with pyenv to that version and make sure you have pytest installed for it. Then you can just run pytest.
- since the pip executable is also among the ones being switched, you need to switch to the alternative Python before installing pytest for it, too.

As I can see, /usr/bin/pytest (that belongs to the system package manager's python-pytest package) has a shebang !#/usr/bin/python since it corresponds to the system python's installation.

pyenv, as its README.md says, does not replace /usr/bin/python - because it indeed should not be replaced to avoid breaking system packages.

Instead, it adds its directory to PATH and inserts a launcher there (called "shim") which is what gets invoked when you type "python". As you probably guessed, this hack is ignored by a shebang like the above - as it should.

Running python -m pytest will make whichever python that launches itself use the package from its installation.
Alternatively, pytest for your other Python version may include versioned executables on the PATH named py.test-<version> (e.g. py.test-3 or py.test-3.6) depending on the way you installed it.
- If it's from a system package manager's package for nonstandard python - like python36-pytest - this is virtually guaranteed.
- I checked that if you install a version with pip, it only creates an unversioned executable (though you can create a versioned one yourself). Moreover, if you install the same package for a different Python version but with the same --prefix, it will overwrite the existing one's executable!
pyenv's suggested way seems to be to install all python versions of interest and packages for them under ~/.pyenv/versions.
- This is not applicable for the system's Python but the default /usr/local can be used for it.
- Once you switch to an alternative Python version, it claims to create shims for all scripts (including pip!) that are currently installed for that version, so invoking those scripts without a path would run those shims.
  - So, if a package (and thus its script) is not installed for the alternative version but installed for system version, trying to run its executable would "fall through" to /usr/local with just the result you're seeing now.

I don't know why but when I run `python -m pytest` I get this error: `/home/meysam/.pyenv/versions/3.5.2/bin/python: No module named pytest` — B Faley, Nov 21 '16 at 13:38
@Meysam that means you didn't install `pytest` for _both_ versions of python (you need to do it separately, you know). — ivan_pozdeev, Nov 21 '16 at 14:07

score 10 · Answer 2 · edited Jul 04 '22 at 11:05

10

I found this related question. For them it worked with this:

python -m pytest tests/my_test.py

I hope it works

edited Jul 04 '22 at 11:05

Neuron

5,141
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answered Nov 21 '16 at 11:50

linpingta

2,324
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I get this error by running the above command: `/home/meysam/.pyenv/versions/3.5.2/bin/python: No module named pytest` – B Faley Nov 21 '16 at 12:18
Have you installed pytest successfully? – linpingta Nov 21 '16 at 13:42
Yes, and all of my tests are passed when I run it. But it only runs under `python 2.7.6`. – B Faley Nov 21 '16 at 13:49
1

Use `python -m pip install pytest` to install pytest in the environment and then try running `python -m pytest` – RealA10N Sep 15 '21 at 16:43

score 1 · Answer 3 · answered Nov 07 '20 at 13:23

I just wanted to run "black" for Python 2.7, but I have installed it in pyenv's Python 3.7.9. It worked correctly with the script /usr/local/bin/black27:

PYENV_VERSION=3.7.9 black -t py27 "$@"

It didn't work with:

pyenv shell 3.7.9
black -t py27 "$@"

nor

pyenv shell 3.7.9
pyenv exec black -t py27 "$@"

pytest running with another version of python

3 Answers3

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