Interpreting type comment is missing, producing different result from flake8

[cielavenir]

Version

$ ruff --version
ruff 0.3.3
$ python3 -m flake8 --version
3.9.2 (flake8_logger: 0.0.0, mccabe: 0.6.1, pycodestyle: 2.7.0, pyflakes: 2.3.1, teamcity-messages: 1.21) CPython 3.9.2 on Linux

Code with import:

import collections


class ToyClass(object):
    dic = None  # type: collections.defaultdict

Result:

$ python3 -m flake8 typecomment1.py 
$ ruff check typecomment1.py 
typecomment1.py:1:8: F401 [*] `collections` imported but unused
Found 1 error.
[*] 1 fixable with the `--fix` option.

Code without import:

class ToyClass(object):
    dic = None  # type: collections.defaultdict

Result:

$ python3 -m flake8 typecomment2.py
typecomment.py:2:17: F821 undefined name 'collections'
$ ruff check typecomment2.py 
All checks passed!

This means that Ruff does not interpret type comment while flake8 does.

I searched for "type comment".

---

Found by a collegue of mine @braineo .

[AlexWaygood]

Thanks for the report!

The latest version of flake8 also does not understand type comments; flake8 3.9.2 is several years old now. It dropped support so that it could improve performance, and because there's no reason to use type comments unless you support very old Python versions that have been end-of-life for a long time. The relevant change here is in one of the builtin flake8 plugins, pyflakes:

• remove handling of # type: comments now that pyflakes is py3+ PyCQA/pyflakes#684

Since great tools such as https://github.com/ilevkivskyi/com2ann exist that can help people auto-upgrade their legacy type comments to type annotations, I'm therefore sceptical that ruff should add support for type comments.

[AlexWaygood]

It looks like this issue is actually a duplicate of #1619, so I'll close in favour of that one 👍

[felixvd]

That's a fair point. Thanks for your prompt and detailed response @AlexWaygood