from datetime import datetime


def get_time_diff(start_time: datetime) -> str:
    """
    Calculates the time difference from a given datetime object and the current time this function is being called.

    Created by Nils Förster.

    :param start_time: The timestamp to calculate the difference from

    :type start_time: datetime

    :returns: The time difference as a formated string.
    :rtype: str

    .. note:: Required packages: datetime
    """

    diff = datetime.now() - start_time
    minutes = divmod(diff.total_seconds(), 60)

    m: str = str(int(minutes[0]))
    s: str = str(int(minutes[1]))
    if minutes[1] < 10:
        s = '0' + s
    return m + ':' + s