python setup.py develop fails with `version = attr: pkg.__version__` in setup.cfg

See also https://github.com/pypa/pip/issues/6350

When a package has version = attr: pkg.__version__ in its setup.cfg file, python setup.py develop can fail with a ModuleNotFoundError if not all runtime dependencies have been installed yet.

I’ve created a minimal repo to reproduce the error: https://github.com/kohr-h/minimal

Reproducing the error:

• Create a fresh environment with python inside, but without numpy (our example dependency)
• Run python setup.py develop in the repo root

Workaround:

• Install numpy as well
• Now python setup.py develop succeeds

Traceback

Traceback (most recent call last):
  File "setup.py", line 3, in <module>
    setup()
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/__init__.py", line 145, in setup
    return distutils.core.setup(**attrs)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/distutils/core.py", line 121, in setup
    dist.parse_config_files()
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/dist.py", line 705, in parse_config_files
    ignore_option_errors=ignore_option_errors)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 120, in parse_configuration
    meta.parse()
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 425, in parse
    section_parser_method(section_options)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 398, in parse_section
    self[name] = value
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 183, in __setitem__
    value = parser(value)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 513, in _parse_version
    version = self._parse_attr(value, self.package_dir)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/site-packages/setuptools/config.py", line 348, in _parse_attr
    module = import_module(module_name)
  File "/home/hkohr/miniconda/envs/tmp/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/hkohr/git/minimal/minimal/__init__.py", line 2, in <module>
    from . import mod
  File "/home/hkohr/git/minimal/minimal/mod.py", line 1, in <module>
    import numpy
ModuleNotFoundError: No module named 'numpy'

---

I wonder whether this can be fixed elegantly and does not sit too deep.

[bsolomon1124]

It seems that as long as you either 1. have no third party imports or 2. point the attr: directive at a literal version = … assignment rather than a derived quantity or something imported, this should just work.

Yes, though one small correction - those two conditions need a boolean-AND, not or 😃. I’m going to venture that 90% of packages that declare a simple one-liner in a module outside of __init__.py turn around and try to import that into __init__.py so that they can bring it directly under the package namespace.

Example:

mkdir pypa-1724
cd pypa-1724
mkdir -p src/package_a
touch README.md
echo '__version__ = "1.0.0"' > src/package_a/_version.py
echo 'import setuptools; setuptools.setup()' > setup.py

cat << EOF > src/package_a/__init__.py
from flask import Flask
from ._version import __version__
EOF

cat << EOF > setup.cfg
[metadata]
name = package-a
version = attr:package_a._version.__version__
description = foo
long_description = file: README.md
long_description_content_type = text/markdown
license = Apache-2.0

[options]
packages = find:
install_requires =
    flask
    importlib_resources;python_version<"3.7"
include_package_data = True
package_dir =
    =src

[options.packages.find]
where = src
EOF

Then:

python3 -m venv venv
. ./venv/bin/activate
python3 -m pip install -e .

Breaks with:

ModuleNotFoundError: No module named 'flask'

whereas removing the flask import in __init__.py (and optionally dropping from install_requires) succeeds, verifiable with python3 -c 'import package_a; print(package_a.__version__)'.

[ThomasTNO]

For future reference, I managed to work around this error by using attr: pkg.__init__.__version__ instead of attr: pkg.__version__.