typevar_bounded.py

from typing import TypeVar, TYPE_CHECKING

BT = TypeVar('BT', bound=float)

def triple2(a: BT) -> BT:
    return a * 3

res2 = triple2(2)

if TYPE_CHECKING:
    reveal_type(res2)

"""
Mypy output:

$ mypy typevar_bounded.py 
typevar_bounded.py:6: error: Incompatible return value type (got "float", expected "BT")
typevar_bounded.py:11: note: Revealed type is "builtins.int*"
Found 1 error in 1 file (checked 1 source file)
$ mypy --version
mypy 0.910
"""