generics_upper_bound.py

"""
Tests TypeVars with upper bounds.
"""

# Specification: https://typing.readthedocs.io/en/latest/spec/generics.html#type-variables-with-an-upper-bound

from typing import Collection, Generic, Sized, TypeVar, assert_type

# > A type variable may specify an upper bound using bound=<type>

T_Good1 = TypeVar("T_Good1", bound=int)  # OK
T_Good2 = TypeVar("T_Good2", bound="ForwardRef | str")  # OK


class ForwardRef: ...


# > <type> itself cannot be parameterized by type variables.

T = TypeVar("T")


class Test(Generic[T]):
    T_Bad1 = TypeVar("T_Bad1", bound=list[T])  # E


ST = TypeVar("ST", bound=Sized)


def longer(x: ST, y: ST) -> ST:
    if len(x) > len(y):
        return x
    else:
        return y


def f(list1: list[int], list2: list[int], set1: set[int], set2: set[int]):
    assert_type(longer(list1, list2), list[int])
    assert_type(longer(set1, set2), set[int])

    # Either answer here is conformant with the spec;
    # exactly one should pass:
    assert_type(longer(list1, set1), list[int] | set[int])  # E[mixed-collections]
    assert_type(longer(list1, set1), Collection[int])  # E[mixed-collections]


def requires_collection(c: Collection[int]) -> None: ...


requires_collection(longer([1], [1, 2]))  # OK

longer(3, 3)  # E


# > An upper bound cannot be combined with type constraints

T_Bad2 = TypeVar("T_Bad2", str, int, bound="int")  # E