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Defining a variable with a type union or optional, etc. and then setting the variable in an extending class overwrites the type of the variable to the narrower type used in the assignment. E.g. int | str to int. If the class is extended again, the type of the variable is the narrower type and can't be broadened again by a simple assignment or changed to another type compatible with the original base class.
To Reproduce
The following code results in an incompatible types in assignment error in the Eggs class:
I would expect the explicitly set type of the base class Spam to be inherited by the first extending class Ham and that an assignment doesn't change the general type of the variable. So that the second extending class can still set var to a str.
Just like the following code is valid:
var: str|intvar=10var="abc"
Actual Behavior
The assignment in Ham sets the type of var to int and the class Eggs can't set var to "abc" of type str.
mypy output: a.py:8: error: Incompatible types in assignment (expression has type "str", base class "Ham" defined the type as "int") [assignment]
Your Environment
Mypy version used: mypy 1.10.0 (compiled: yes)
Python version used: Python 3.12.3 (main, Apr 23 2024, 09:16:07) [GCC 13.2.1 20240417] on linux
The text was updated successfully, but these errors were encountered:
Bug Report
Defining a variable with a type union or optional, etc. and then setting the variable in an extending class overwrites the type of the variable to the narrower type used in the assignment. E.g.
int | str
toint
. If the class is extended again, the type of the variable is the narrower type and can't be broadened again by a simple assignment or changed to another type compatible with the original base class.To Reproduce
The following code results in an incompatible types in assignment error in the
Eggs
class:Expected Behavior
I would expect the explicitly set type of the base class
Spam
to be inherited by the first extending classHam
and that an assignment doesn't change the general type of the variable. So that the second extending class can still setvar
to a str.Just like the following code is valid:
Actual Behavior
The assignment in
Ham
sets the type ofvar
toint
and the classEggs
can't setvar
to"abc"
of typestr
.mypy output:
a.py:8: error: Incompatible types in assignment (expression has type "str", base class "Ham" defined the type as "int") [assignment]
Your Environment
mypy 1.10.0 (compiled: yes)
Python 3.12.3 (main, Apr 23 2024, 09:16:07) [GCC 13.2.1 20240417] on linux
The text was updated successfully, but these errors were encountered: