AttributeError: module 'setuptools.build_meta' has no attribute '__legacy__'

I’m trying to install project I’m working on using pip3 install -e "file:///home/vagrant/devel", but everytime I end up with:

$> pip3 install -e "file:///home/vagrant/devel"
Obtaining file:///home/vagrant/devel
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  Complete output from command /home/vagrant/.virtualenvs/anitya/bin/python3 /home/vagrant/.virtualenvs/anitya/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmp6db90a_q:
  Traceback (most recent call last):
    File "/home/vagrant/.virtualenvs/anitya/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py", line 207, in <module>
      main()
    File "/home/vagrant/.virtualenvs/anitya/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py", line 197, in main
      json_out['return_val'] = hook(**hook_input['kwargs'])
    File "/home/vagrant/.virtualenvs/anitya/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py", line 48, in get_requires_for_build_wheel
      backend = _build_backend()
    File "/home/vagrant/.virtualenvs/anitya/lib/python3.7/site-packages/pip/_vendor/pep517/_in_process.py", line 39, in _build_backend
      obj = getattr(obj, path_part)
  AttributeError: module 'setuptools.build_meta' has no attribute '__legacy__'

Maybe I’m just doing something wrong, but this worked few days ago.

[pganssle]

As far as I know, this is triggered when all of the following conditions are met:

1. You are using a virtualenv with --system-site-packages
2. You are using pip >= 19.0.2
3. Your system version of setuptools is less than 40.8.0.
4. The package you are installing does not specify build-backend="setuptools.build_meta" in its pyproject.toml.

It is a bug in pip’s PEP 517 build isolation code: pypa/pip#6264.

The best way to fix it at the moment is to explicitly specify build-backend="setuptools.build_meta" in your pyproject.toml, like this. Note that you’ll also want to put pyproject.toml in your MANIFEST.in.

Assuming you need --system-site-packages in your virtualenv, the second best way to solve this is to upgrade your system version of setuptools.

I’m going to close this issue as not a bug in setuptools, but thank you for the report. I recommend giving a +1 on the pip thread, or chiming in there if you managed to trigger this in a different way.

[pganssle]

@Zlopez Oh, also pip install -e --no-use-pep517 'file://whatever/vagrant/devel' may work, not sure - I think it depends on whether the package in question was relying on the PEP 518 dependency satisfaction or not.