Use Final instead of Literal in logging

[srittau]

No description provided.

[srittau]

Test for #7258

[Akuli]

You need to import Final.

[srittau]

The flake8 error was expected, the pytype one not.

[AlexWaygood]

An encouraging primer output, however

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pip (https://github.com/pypa/pip)
- src/pip/_internal/locations/__init__.py:68: error: Incompatible types in assignment (expression has type "Literal[10]", variable has type "Literal[30]")
- src/pip/_internal/utils/logging.py:231: error: Incompatible types in assignment (expression has type "int", variable has type "Literal[10]")
- src/pip/_internal/utils/logging.py:233: error: Incompatible types in assignment (expression has type "Literal[30]", variable has type "Literal[10]")
- src/pip/_internal/utils/logging.py:235: error: Incompatible types in assignment (expression has type "Literal[40]", variable has type "Literal[10]")
- src/pip/_internal/utils/logging.py:237: error: Incompatible types in assignment (expression has type "Literal[50]", variable has type "Literal[10]")
- src/pip/_internal/utils/logging.py:239: error: Incompatible types in assignment (expression has type "Literal[20]", variable has type "Literal[10]")
- src/pip/_internal/utils/subprocess.py:125: error: Incompatible types in assignment (expression has type "int", variable has type "Literal[20]")

streamlit (https://github.com/streamlit/streamlit)
- lib/streamlit/logger.py: note: In function "set_log_level":
- lib/streamlit/logger.py:41:21: error: Incompatible types in assignment (expression has type "Literal[40]", variable has type "Literal[50]")  [assignment]
- lib/streamlit/logger.py:43:21: error: Incompatible types in assignment (expression has type "Literal[30]", variable has type "Literal[50]")  [assignment]
- lib/streamlit/logger.py:45:21: error: Incompatible types in assignment (expression has type "Literal[20]", variable has type "Literal[50]")  [assignment]
- lib/streamlit/logger.py:47:21: error: Incompatible types in assignment (expression has type "Literal[10]", variable has type "Literal[50]")  [assignment]
- lib/streamlit/logger.py:57:17: error: Incompatible types in assignment (expression has type "Literal[50]", variable has type "Literal[20]")  [assignment]

[hauntsaninja]

mypy_primer did tell us this was going to be a problem in #6610 and we merged, acknowledging that we might want to revert later. Maybe this question isn't meaningful, but do we feel like "this is things going to plan: we tried a thing, it didn't work" or should we update in the direction of being less likely to merge past primer issues?

[srittau]

Closing due to the discussion in #7258.