from typing import Union
from typing import Callable


def _get_callable_str(*, callable_: Union[Callable, str]) -> str:
    """
    Get a callable string (label).

    Parameters
    ----------
    callable_ : Callable or str
        Target function or method or property or dunder method name.

    Returns
    -------
    callable_str : str
        A callable string (label).
    """
    if isinstance(callable_, str):
        callable_str: str = callable_
    else:
        callable_str = callable_.__name__
    return callable_str