[Python] How to annotate mutable structures for Mypy

I have this code:

def my_foo(x: dict[str, int | float], some_condition: bool) -> None:
if some_condition:
x['the_int'] = 1
else:
x['the_float'] = 1.0

my_dict = {'some_int': 2}

my_foo(my_dict, True)


Mypy (understandably) complains

error: Argument 1 to "my_foo" has incompatible type "dict[str, int]"; expected "dict[str, int | float]" [arg-type] note: "Dict" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance src\type_test.py:23: note: Consider using "Mapping" instead, which is covariant in the value type
​

I tried do type-hint using MutableMapping but to no avail:

error: Argument 1 to "my_foo" has incompatible type "dict[str, int]"; expected "MutableMapping[str, int | float]"
​

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