from collections.abc import Iterable, Hashable, Mapping
from typing import TypeVar, Any
K = TypeVar("K", bound=Hashable)
def func1(data: Iterable[K]) -> Mapping[K, Any]:
t_dict = {k: 0 for k in data}
return t_dict
def func2(data: Iterable[Hashable]) -> Mapping[Hashable, Any]:
t_dict = {k: 0 for k in data}
return t_dict
if __name__ == '__main__':
data1 = [[1, 2, 3] * 3]
func1(data1)
func2(data1)
""" What is the difference between TypeVar(bound=Hashable) and just Hashable. How it work? """
Occurrences of the abstract base class Hashable (or indeed any class) in the type signature are independent: each one can refer to a completely different type:
def foo(x: Hashable) -> Hashable:
return 3
This type-checks because no matter what hashable value you pass as an argument, 3 (as an int) is a hashable value.
Type variables must be bound to the same class in each occurrence.
def bar(x: K) -> K:
return 3
This definition does not type-check because an int is only a valid return value if an int is passed as an argument.