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main.py

from typing import *

K_contra = TypeVar("K_contra", contravariant=True)
K_co = TypeVar("K_co", covariant=True)
V_co = TypeVar("V_co", covariant=True)
V = TypeVar("V")
T = TypeVar("T")

class ContravariantMapping(Protocol[K_contra, V_co]):
    def __getitem__(self, __key: K_contra) -> V_co: ...
    @overload
    def get(self, __key: K_contra) -> V_co | None: ...
    @overload
    def get(self, __key: K_contra, default: V_co | T) -> V_co | T: ...
    def values(self) -> ValuesView[V_co]: ...
    def __contains__(self, __o: object) -> bool: ...
    def __len__(self) -> int: ...
    
    
class CovariantMapping(Protocol[K_co, V_co]):
    def items(self) -> ItemsView[K_co, V_co]: ...
    def keys(self) -> KeysView[K_co]: ...
    def values(self) -> ValuesView[V_co]: ...
    def __contains__(self, __o: object) -> bool: ...
    def __iter__(self) -> Iterator[K_co]: ...
    def __len__(self) -> int: ...
    
    
class ContravariantMutableMapping(Protocol[K_contra, V]):
    def __setitem__(self, __key: K_contra, __value: V) -> None: ...
    def __getitem__(self, __key: K_contra) -> V: ...
    @overload
    def get(self, __key: K_contra) -> V | None: ...
    @overload
    def get(self, __key: K_contra, default: V | T) -> V | T: ...
    def values(self) -> ValuesView[V]: ...
    def __contains__(self, __o: object) -> bool: ...
    def __len__(self) -> int: ...


a: Dict[int, str]
b: Dict[float, str]

c: CovariantMapping[float, str] = a
c.items()
c[0.0]  # error, not covariant, if you pass a is actually a Mapping[int, str], doing an index with a float might not be safe

d: ContravariantMapping[int, str] = b
d[0]
d.keys()  # error, says it would return an iterable of int, but b is a Dict[float], so it will unsafely return floats

e: ContravariantMutableMapping[int, str] = b
e[0] = "wew"