Add a `per-file-target-version` configuration option

[dmarteau]

Feature

Add a per-file-target-version configuration option like Ruff

Pitch

Actually there is no way with Mypy to enforce python compatibility with older version while having specific parts of code for newer version.

Example:

• I have a project that must be still globally compatible with Python 3.9, but I include some code that would work with Python 3,12.
• My testing environment is Python 3,12.
• Because I want Python 3.9 compatibility I set python_version option to 3.9.
• Part of the code the support python 3.12 may use if sys.version >= (3, 12) but because my testing environment is 3,12, this statement has no effect and Mypy treat the 3.12 code as en error while it should be checked against 3.12.

[wyattscarpenter]

I don't have strong feelings about this; but, for the purposes of clarifying the issue: do you think https://mypy.readthedocs.io/en/stable/config_file.html#confval-python_version would work for you if it were allowed per-module (per file)? Or perhaps as an inline configuration?

[A5rocks]

Mypy treat the 3.12 code as en error while it should be checked against 3.12.

mypy should ignore 3.12 code if run with python_version 3.9. What does your code look like?

[dmarteau]

do you think https://mypy.readthedocs.io/en/stable/config_file.html#confval-python_version would work for you if it were allowed per-module (per file)?

I think so, At first glance it would behave like the Ruff per-file-target-version setting.

[dmarteau]

Mypy treat the 3.12 code as en error while it should be checked against 3.12.

mypy should ignore 3.12 code if run with python_version 3.9. What does your code look like?

Its a match statement in a module which is imported contditionally, Mypy gives the following error:

lizmap_server/context/qjazz.py:70: error: Pattern matching is only supported in Python 3.10 and greater  [syntax]

Bracketing the code with sys.version_info >= 3.10 does not change anything since my environment is Python 3.12 and this condition is always True.

[dmarteau]

What does your code look like?

The code is here: https://github.com/3liz/qgis-lizmap-server-plugin/blob/code-enhancement/lizmap_server/context/qjazz.py#L56

This module is loaded only when some condition are met.

[A5rocks]

IMO the error is a bug. I think per file target versions is a pretty strange configuration option to have when we already support

assert sys.version_info >= (3, 10)

[dmarteau]

IMO the error is a bug. I think per file target versions is a pretty strange configuration option to have when we already support

assert sys.version_info >= (3, 10)

Nor the conditiion nor the assertion prevent the [syntax] error (just checked). But if that worked, and Mypy would check against the specified version, I agree that it would be the same as having a per file target version.

The Mypy version used is 1.18.2