pip install fails with .../python3: can't find '__main__' module in '.../pep517/_in_process.py

[lazka]

Environment

• pip version: 20.0.2
• Python version: 3.8.2
• OS: Ubuntu 20.04 and Debian testing/sid

Description

Sometime during the last week or two installing pygobject with pip has started to fail with (full log at the bottom):

python3: can't find '__main__' module in '/home/lazka/Desktop/git/pygobject/_venv/share/python-wheels/pep517-0.7.0-py2.py3-none-any.whl/pep517/_in_process.py'

This is before any of my setup.py code is executed so I don't know what is going on.

The only workaround I found so far is removing the "pyproject.toml" file which currently contains this:

[build-system]
requires = ["setuptools", "wheel", "pycairo"]

Expected behavior

pip install succeeds like it did before

How to Reproduce

• In a venv install pygobject: pip install pygobject
• Note that this needs some system packages on Debian/Ubuntu: sudo apt install libgirepository1.0-dev gcc libcairo2-dev pkg-config python3-dev

Output

> pip install .
Processing /home/lazka/Desktop/git/pygobject
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  ERROR: Command errored out with exit status 1:
   command: /home/lazka/Desktop/git/pygobject/_venv/bin/python3 /home/lazka/Desktop/git/pygobject/_venv/share/python-wheels/pep517-0.7.0-py2.py3-none-any.whl/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpopma5aoh
       cwd: /tmp/pip-req-build-htjk5uuc
  Complete output (1 lines):
  /home/lazka/Desktop/git/pygobject/_venv/bin/python3: can't find '__main__' module in '/home/lazka/Desktop/git/pygobject/_venv/share/python-wheels/pep517-0.7.0-py2.py3-none-any.whl/pep517/_in_process.py'
  ----------------------------------------
ERROR: Command errored out with exit status 1: /home/lazka/Desktop/git/pygobject/_venv/bin/python3 /home/lazka/Desktop/git/pygobject/_venv/share/python-wheels/pep517-0.7.0-py2.py3-none-any.whl/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpopma5aoh Check the logs for full command output.

[lazka]

I've created a minimal reproducer: https://github.com/lazka/pip-pyproject-bug

Just a basic pyproject.toml fails. I wonder why I'm the first to hit this, hm.

[lazka]

Another data point: This doesn't fail on Arch Linux with the same pip/python, so might be a Debian only issue.

[lazka]

Turns out forcing a pip install with "--force-reinstall" in the venv makes things work, so this is a broken pip in Debian which was also pulled into Ubuntu. I'll report this to Debian instead.

[uranusjr]

Looks similar to #7874 (see sqlalchemy/sqlalchemy#5207). This is indeed a Debian issue, they patch parts of the Python standard distribution that makes PEP 517 fail. Please definitely report this to Debian; they are in the best position to fix this.

In the mean time, there are workarounds in the linked issues to avoid force-reinstall pip.

[lazka]

I've reported it to Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=955414