Bug Report
When doing pattern matching with types, the match statement might be more readable than multiple if statements
match (a is None, b is None):
case (True, True):
...
case (True, False):
...
case (False, True):
...
case (False, False):
...instead of
if a is None and b is None:
...
if a is None and b is not None:
...
if a is not None and b is None:
...
if a is not None and b is not None:
...However, mypy is not able to infer types from the match statements like it is from if statements.
To Reproduce
Infer types using a match statement:
def example_with_match(a: str | None, b: str | None) -> str:
match (a is None, b is None):
case (True, True):
return ""
case (True, False):
return b
case (False, True):
return a
case (False, False):
return a + b
raise RuntimeError # unreachableGist
Expected Behavior
Like in the equivalent using if statements (there are no mypy errors)
def example_with_if(a: str | None, b: str | None) -> str:
if a is None and b is None:
return ""
if a is None and b is not None:
return b
if a is not None and b is None:
return a
if a is not None and b is not None:
return a + b
raise RuntimeError # unreachableGist
Actual Behavior
whatever.py:6: error: Incompatible return value type (got "str | None", expected "str") [return-value]
whatever.py:8: error: Incompatible return value type (got "str | None", expected "str") [return-value]
whatever.py:10: error: Unsupported operand types for + ("str" and "None") [operator]
whatever.py:10: error: Unsupported left operand type for + ("None") [operator]Your Environment
- Mypy version used: 1.15.0
- Mypy command-line flags: None
- Mypy configuration options from mypy.ini (and other config files):
[tool.mypy]
check_untyped_defs = true
no_implicit_optional = true
show_error_codes = true
warn_redundant_casts = true
warn_unreachable = true
python_version = "3.12"
ignore_missing_imports = true
- Python version used: 3.12.8
Bug Report
When doing pattern matching with types, the match statement might be more readable than multiple if statements
instead of
However, mypy is not able to infer types from the match statements like it is from if statements.
To Reproduce
Infer types using a match statement:
Gist
Expected Behavior
Like in the equivalent using if statements (there are no mypy errors)
Gist
Actual Behavior
Your Environment