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non-writeable property name in IO #2824

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Description

@jolaf

I'm trying to create my own class that has IO capability.
The class instances would have names similar to file names, but specified at the moment of instance creation.
However when I try setting name field, mypy is protesting.

Here's the minimal repro:

from typing import AnyStr, IO
class MyIO(IO[AnyStr]):
    def __init__(self, name: str) -> None:
        self.name = name

mypy output:

Test.py: note: In member "__init__" of class "MyIO":
Test.py:5: error: Property "name" defined in "IO" is read-only

Activity

  1. srittau commented on Mar 5, 2019

    @srittau
    Collaborator

    IO.name is defined as a property in both the typing implementation and the stubs. You need to override this property in your sub-class if you want to provide a setter:

    from typing import AnyStr, IO
    
    class MyIO(IO[AnyStr]):
        def __init__(self, name: str) -> None:
            self.name = name
    
        @property
        def name(self) -> str:
            ...
    
        @name.setter
        def name(self, name: str) -> None:
            ...
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