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Inference for Literal arguments not handled #11003
Description
Bug Report
If you have a function with Literal arguments, and a variable that is set to one of the options, an error is reported.
To Reproduce
from typing import Literal
def myfun(a: Literal["a", "b", "c"]) -> str:
return a
s = "a"
myfun(s)
def myfun2(a: Literal[1, 2]) -> int:
return a
b = 2
myfun2(b)
c = 1 if s == "a" else 2
myfun2(c)reports
literalinf.py:10: error: Argument 1 to "myfun" has incompatible type "str"; expected "Union[Literal['a'], Literal['b'], Literal['c']]"
literalinf.py:18: error: Argument 1 to "myfun2" has incompatible type "int"; expected "Union[Literal[1], Literal[2]]"
literalinf.py:21: error: Argument 1 to "myfun2" has incompatible type "int"; expected "Union[Literal[1], Literal[2]]"
Expected Behavior
No error. The values can be inferred to be of the Literal value
Actual Behavior
See above.
Your Environment
- Mypy version used: 0.910
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.8.5
- Operating system and version: Windows 10 21H1
Activity
emmatyping commentedon Aug 20, 2021
The problem is if the variable is re-assigned to, then it could be incorrect to pass it to these functions. The solution for your scenario is to type these assignments with Final, like
a: Final = "a".erictraut commentedon Aug 20, 2021
It shouldn't be necessary to mark them as Final. If a variable is reassigned, the type checker knows it's reassigned and can flag it as an error.
There is no type violation, so these errors are false positives.
The above code type checks without errors in pyright. I don't see why it shouldn't work with mypy.
Dr-Irv commentedon Aug 21, 2021
I agree. @ethanhs based on @erictraut 's comment, can you reopen this?
Zac-HD commentedon Dec 10, 2021
I get a related error when setting the default argument to a function:
hauntsaninja commentedon Dec 10, 2021
Hello @Zac-HD ! I enjoyed your recent paper :-) The default arguments issue is fixed on master, in #11236
Zac-HD commentedon Dec 10, 2021
Thanks, and thanks! I'm really looking forward to 0.920 and the release after 😁