import time


def time_spent_from(start_time: float) -> float:
    """Calculate time spent from start_time to now

    Example:
    >>> start_time = time.time()
    >>> ...
    >>> time_spent = time_spent_from(start_time)

    :param start_time: time in seconds since the epoch
    :return: time spent from start_time to now
    """
    return time.time() - start_time