TypeError: Item in ``from list'' must be str, not NoneType

[konstin]

I'm trying to add PEP 517 support to a packaging tool I've written (pyo3-pack) and I when I tried to test sdist support with tox, I got a TypeError inside tox code.

pyproject.toml

[build-system]
requires = ["/path/to/current/dev/build/pyo3_pack-0.6.1-py2.py3-none-manylinux1_x86_64.whl", "toml"]
build-backend = "pyo3_pack"

[tool.pyo3-pack]
bindings = "cffi"

tox.ini

[tox]
envlist = py35,py36,py37
isolated_build = True

[testenv]
deps = pytest cffi
commands = pytest

Running leads to the following output:

$ tox -rvv
using tox.ini: /home/konsti/pyo3-pack/test-crates/cffi-pure/tox.ini (pid 9495)
using tox-3.12.1 from /home/konsti/pyo3-pack/venv/lib/python3.6/site-packages/tox/__init__.py (pid 9495)
.package start: getenv /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package
.package cannot reuse: -r flag
.package create: /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package
/home/konsti/pyo3-pack/venv/bin/python (/home/konsti/pyo3-pack/venv/bin/python) is {'executable': '/home/konsti/pyo3-pack/venv/bin/python', 'name': 'python', 'version_info': [3, 6, 8, 'final', 0], 'version': '3.6.8 (default, Jan 14 2019, 11:02:34) \n[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]]', 'is_64': True, 'sysplatform': 'linux'}
.package uses /home/konsti/pyo3-pack/venv/bin/python
setting PATH=/home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin:/home/konsti/pyo3-pack/venv/bin:/home/konsti/.pyenv/bin:/home/konsti/.pyenv/plugins/pyenv-virtualenv/shims:/home/konsti/.pyenv/shims:/home/konsti/.nvm/versions/node/v10.5.0/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/konsti/.cargo/bin:/home/konsti/.local/bin
[9502] /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox$ /home/konsti/pyo3-pack/venv/bin/python -m virtualenv --no-download --python /home/konsti/pyo3-pack/venv/bin/python .package
Already using interpreter /home/konsti/pyo3-pack/venv/bin/python
Using base prefix '/usr'
New python executable in /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin/python
Installing setuptools, pip, wheel...
done.
.package installdeps: /home/konsti/pyo3-pack/target/wheels/pyo3_pack-0.6.1-py2.py3-none-manylinux1_x86_64.whl, toml
setting PATH=/home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin:/home/konsti/pyo3-pack/venv/bin:/home/konsti/.pyenv/bin:/home/konsti/.pyenv/plugins/pyenv-virtualenv/shims:/home/konsti/.pyenv/shims:/home/konsti/.nvm/versions/node/v10.5.0/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/konsti/.cargo/bin:/home/konsti/.local/bin
[9511] /home/konsti/pyo3-pack/test-crates/cffi-pure$ /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin/python -m pip install /home/konsti/pyo3-pack/target/wheels/pyo3_pack-0.6.1-py2.py3-none-manylinux1_x86_64.whl toml
Processing /home/konsti/pyo3-pack/target/wheels/pyo3_pack-0.6.1-py2.py3-none-manylinux1_x86_64.whl
Collecting toml
  Using cached https://files.pythonhosted.org/packages/a2/12/ced7105d2de62fa7c8fb5fce92cc4ce66b57c95fb875e9318dba7f8c5db0/toml-0.10.0-py2.py3-none-any.whl
Installing collected packages: pyo3-pack, toml
Successfully installed pyo3-pack-0.6.1 toml-0.10.0
.package finish: getenv /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package after 4.66 seconds
.package start: finishvenv 
write config to /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/.tox-config1 as '94aaba361509f3eb875f759baaad9c10 /home/konsti/pyo3-pack/venv/bin/python\n3.12.1 0 0 0\n9a98df95e2f78ca59a589cb2f3e1099f /home/konsti/pyo3-pack/target/wheels/pyo3_pack-0.6.1-py2.py3-none-manylinux1_x86_64.whl\n00000000000000000000000000000000 toml'
.package finish: finishvenv  after 0.03 seconds
.package start: get-build-requires /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package
setting PATH=/home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin:/home/konsti/pyo3-pack/venv/bin:/home/konsti/.pyenv/bin:/home/konsti/.pyenv/plugins/pyenv-virtualenv/shims:/home/konsti/.pyenv/shims:/home/konsti/.nvm/versions/node/v10.5.0/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/konsti/.cargo/bin:/home/konsti/.local/bin
[9518] /home/konsti/pyo3-pack/test-crates/cffi-pure$ /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin/python /home/konsti/pyo3-pack/venv/lib/python3.6/site-packages/tox/helper/build_requires.py pyo3_pack '' >.tox/.package/log/.package-0.log
ERROR: invocation failed (exit code 1), logfile: /home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/log/.package-0.log
================================================================================= log start =================================================================================
Traceback (most recent call last):
  File "/home/konsti/pyo3-pack/venv/lib/python3.6/site-packages/tox/helper/build_requires.py", line 7, in <module>
    backend = __import__(backend_spec, fromlist=[None])
  File "<frozen importlib._bootstrap>", line 1014, in _handle_fromlist
TypeError: Item in ``from list'' must be str, not NoneType

================================================================================== log end ==================================================================================
ERROR: FAIL could not package project - v = InvocationError("/home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin/python /home/konsti/pyo3-pack/venv/lib/python3.6/site-packages/tox/helper/build_requires.py pyo3_pack ''", 1)

The module that code tries to import is importable (/home/konsti/pyo3-pack/test-crates/cffi-pure/.tox/.package/bin/python -c "import pyo3_pack" passes). If I replace the failing line with backend = __import__(backend_spec, fromlist=[]) or backend = __import__(backend_spec), the error disappears. The current WIP PEP 517 implementation is at pyo3_pack/__init__.py, the failing code was introduce in #1145.

[konstin]

I created a minimal example at https://github.com/konstin/tox-1344:

git clone https://github.com/konstin/tox-1344
cd tox-1344
python3 -m venv venv
source venv/bin/activate
pip install tox
tox

This prints:

.package create: /home/konsti/tox-1344/.tox/.package
.package installdeps: pyo3-pack==0.7.0-beta.4, toml
ERROR: invocation failed (exit code 1), logfile: /home/konsti/tox-1344/.tox/.package/log/.package-2.log
================================================================================= log start =================================================================================
Traceback (most recent call last):
  File "venv/lib/python3.6/site-packages/tox/helper/build_requires.py", line 7, in <module>
    backend = __import__(backend_spec, fromlist=[None])
  File "<frozen importlib._bootstrap>", line 1014, in _handle_fromlist
TypeError: Item in ``from list'' must be str, not NoneType

================================================================================== log end ==================================================================================
ERROR: FAIL could not package project - v = InvocationError("/home/konsti/tox-1344/.tox/.package/bin/python venv/lib/python3.6/site-packages/tox/helper/build_requires.py pyo3_pack ''", 1)

tox --version: 3.13.2 imported from /home/konsti/tox-1344/venv/lib/python3.6/site-packages/tox/__init__.py

GitHub

konstin/tox-1344

Contribute to konstin/tox-1344 development by creating an account on GitHub.

[gaborbernat]

I think we left out this part from pep 517: It's also legal to leave out the :object part, e.g.

[thedrow]

So how can we fix it?

[gaborbernat]

Feel free to open a PR against master and fix it. My available efforts at the moment are aimed at fixing this as part of #1394, but that probably will take a while (ETA September).