python / python/mypy

Wrong errors of type unsupported operand when type checking is done in list

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Beschreibung

Bug Report

(A clear and concise description of what the bug is.)

To Reproduce

a: None | float = 0.0
b: None | float = 0.0

c = None if None in (a, b) else a - b
print(c)

(Also the alternative approach of using a regular if...else... block fails)

Playground link

Expected Behavior

No error found by mypy. I cannot think of a way that this code fails. But maybe I'm just very code-blind right now.

Actual Behavior

coordinate_magic/test.py:4: error: Unsupported left operand type for - ("None")  [operator]
coordinate_magic/test.py:4: error: Unsupported operand types for - ("None" and "float")  [operator]
coordinate_magic/test.py:4: error: Unsupported operand types for - ("float" and "None")  [operator]
coordinate_magic/test.py:4: note: Both left and right operands are unions
Found 3 errors in 1 file (checked 1 source file)

Your Environment

  • Mypy version used: mypy 1.8.0 (compiled: yes)
  • Mypy command-line flags: None
  • Mypy configuration options from mypy.ini (and other config files): pyproject.toml
    [tool.mypy]
    # Config for 'mypy'
    # See https://mypy.readthedocs.io/en/stable/config_file.html#using-a-pyproject-toml-file for more details
    python_version = "3.11"
    plugins = "numpy.typing.mypy_plugin"
    warn_return_any = true
    warn_unused_configs = true
    allow_redefinition = true        # Allows variables to be redefined with an arbitrary type, as long as the redefinition is in the same block and nesting level as the original definition.
    disallow_untyped_defs = true
    disallow_incomplete_defs = true  # Disallows defining functions with incomplete type annotations.
    check_untyped_defs = true        # Type-checks the interior of functions without type annotations.
    no_implicit_optional = true      # Changes the treatment of arguments with a default value of None by not implicitly making their type Optional.
    show_error_codes = true
    exclude = "gui/|doc/|coordinate.py"
    
    [[tool.mypy.overrides]]
    # mypy per-module options
    module = [
        "scipy",
        "scipy.*",
        "mpl_toolkits.mplot3d",
        "altair",       # Remove when issue https://github.com/altair-viz/altair/issues/2493 is solved
        "folium",       # Remove when issue https://github.com/python-visualization/folium/issues/1559 is solved
        "folium.plugins",
        "matplotlib",   # Remove when issue https://github.com/matplotlib/matplotlib/issues/20504 is solved
        "matplotlib.*",
        "traffic",
        "coloredlogs",  # Remove when issue https://github.com/xolox/python-coloredlogs/issues/93 is solved
        "pymap3d",      # Remove when discussion https://github.com/geospace-code/pymap3d/pull/76 is solved
    ]
    ignore_missing_imports = true
    
  • Python version used: 3.11

The problem lies in the if None in (a, b) part.
As soon as code is changed to

a: None | float = 0.0
b: None | float = 0.0

c = None if a is None or b is None else a - b
print(c)

mypy does not report an error.

EDIT: Added a playground link with all examples

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Rechercherichtung

Reproduziere das Snippet aus coordinate_magic/test.py mit mypy 1.8.0 und vergleiche anschließend die Form None in (a, b) mit der Form is None. Untersuche den Typprüfungsweg für die auf Mitgliedschaft basierende Eingrenzung; abgeschlossen ist die Arbeit, wenn die gültige Subtraktion keine unsupported-operand-Fehler mehr erzeugt und die Regression durch einen Test abgedeckt ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Bewertung

Tech-Stack
python
Bereich
compilers
Issue-Typ
Bug
Schwierigkeit
4/5
Geschätzter Aufwand
3-5 Tage
Aktivitätsstatus
Veraltet
Klarheit
Größtenteils klar
Anfängerfreundlichkeit
42/100

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