first_digit_by_str.py

def first_digit(number: int) -> int:
    """
    >>> first_digit(-123)
    1
    >>> first_digit(0)
    0
    >>> first_digit(123)
    1
    >>> first_digit(123456789)
    1
    """
    return int(str(abs(number))[0])


if __name__ == "__main__":
    from doctest import testmod

    testmod()