Python min-function example implementation

min.py

#!/usr/bin/env python3

from typing import Callable, Iterable, T

def my_min(iterable: Iterable[T], key: Callable[[T, ...], Any]=lambda x: x) -> T:

    iterator = iter(iterable)

    try:
        lowest = key(next(iterator))
    except StopIteration:
        raise ValueError("Iterable is empty")

    for value in iterator:
        value = key(value)
        if lowest > value:
            lowest = value

    return lowest