Fix isolated build helper scripts

[davidhewitt]

Fixes #1344

The PEP 517 isolated build uses these helper scripts, but they invoke the __import__ builtin incorrectly.

[gaborbernat]

.

[gaborbernat]

Requires tests 👍 The changelog is added via towncrier not directly, see example.rst.

[davidhewitt]

Ah shoot, I'll remove CHANGELOG edit and use towncrier. Also will figure out CI issue.

[asottile]

this should be fromlist=['_trash']

[davidhewitt]

👍 - Though also I think the "right" answer on Python 3.3 and above is to use importlib.import_module. So I'll split this into two branches, so that this __import__ branch can be removed once support for old Python versions is removed.

[asottile]

I disagree, please just use __import__, no need to involve a separate module to do exactly the same thing

[davidhewitt]

As for adding tests, I'd appreciate any suggestions on how a testing strategy could be established here.

The "problem case" which this PR fixes is when the backend_spec is just a base package, e.g. no submodule:

>>> __import__('setuptools.build_meta', fromlist=[None])
<module 'setuptools.build_meta' from '...'>

>>> __import__('setuptools', fromlist=[None])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<frozen importlib._bootstrap>", line 1033, in _handle_fromlist
TypeError: Item in ``from list'' must be str, not NoneType

I'm not aware of any PEP 517 backends other than maturin which are just a base package and so could be used to write an integration test for this. maturin will be messy to write a test for, because it requires a Rust library to compile.

As such - any advice on suitable testing strategy here?

[gaborbernat]

For tests you can provide an inline back end and define that to not have that part. There's another pr open for that you could check it out. By the way Ive tried maturin last week and liked it 🙏

[davidhewitt]

I've reverted to just use __import__ as requested. Thanks for the testing advice - I'll try to find time to write a test as described tomorrow evening.

By the way Ive tried maturin last week and liked it 🙏

\o/ glad to hear!

[davidhewitt]

Test successfully added and lint fixed. I think this might be good to go?

[gaborbernat]

[gaborbernat]

@davidhewitt released https://pypi.org/project/tox/3.18.1