Created
June 14, 2021 12:36
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Proper annotation of python's add operator
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"""An example of how deep python annotations can go. | |
Here I show a possible way to annotate an add() function to account for as many cases as possible. | |
We assume that the add() function simply adds the two numbers and does not call internal __add__ or __radd__ methods. | |
""" | |
from typing import Protocol, overload | |
T_contra = TypeVar('T_contra', contravariant=True) | |
T_co = TypeVar('T_co', covariant=True) | |
class SupportsAdd(Protocol[T_contra, T_co]): | |
def __add__(self, x: T_contra) -> T_co: ... | |
class SupportsRAdd(Protocol[T_contra, T_co]): | |
def __radd__(self, x: T_contra) -> T_co: ... | |
@overload | |
def add(x: SupportsAdd[T_contra, T_co], y: T_contra) -> T_co: ... | |
@overload | |
def add(x: T_contra, y: SupportsRAdd[T_contra, T_co]) -> T_co: ... | |
def add(x, y): | |
return x + y |
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