CODEWITHSUNDEEP
pythontype-hintingmypy
Olivier RD
Olivier RD

Reputation: 699

Python: All type hints errors in subclass constructure seems ignored

I have the following code with python type hints It has a bunch of errors. All erros in code are found by mypy but not the errors in constructor of S. Why? I cannot find out what is happening thanks

code:

import typing

class T(object):
    def __init__(self, a: int, b: str = None) -> None:
        self.a = a
        self.b: typing.Union[str, None] = b
        self._callback_map: typing.Dict[str, str] = {}


class S(T):
    def __init__(self):
        super().__init__(self, 1, 2)
        self._callback_map[1] = "TOTO"
        s = T(1, 1)
        t = T(1, b=2)
        t._callback_map[2] = "jj"


s = T(1, 2)

t = T(1, b=2)
t._callback_map[2] = "jj"

output of mypy: 

 t.py:22: error: Argument 2 to "T" has incompatible type "int"; expected "Optional[str]"
t.py:24: error: Argument "b" to "T" has incompatible type "int"; expected "Optional[str]"
rt.py:25: error: Invalid index type "int" for "Dict[str, str]"; expected type "str"

This is fine, but the same errors (same lines) in 'init' at line 16, 17, 18 are not found at all...

Upvotes: 0

Views: 696

Answers (1)

Michael0x2a
Michael0x2a

Reputation: 64178

Mypy, by default, will only check functions and methods that have type annotations.

Your subclass's constructor has no annotations and so consequently goes unchecked.

To fix this, modify the signature to read def __init__(self) -> None.

You can also ask mypy to flag these errors for you using the --disallow-untyped-defs flag. You can also use the --check-untyped-defs flag which will make it typecheck all functions, whether or not it has annotations.

Upvotes: 1

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