def format_span(start, end):
    """
    Format a time span into a human-friendly string.

    Parameters
    ----------
    start : datetime
    end : datetime

    Returns
    -------
    str
        Formatted time span.

    Examples
    --------
    >>> from datetime import datetime
    >>> from tomputils import mattermost as mm
    >>> start = datetime(2017,4,1,12,55,1)
    >>> end = datetime(2017,4,2,2,20,1)
    >>> print(mm.format_span(start, end))
    04/01/2017 12:55:01 - 02:20:01
    >>>

    """
    time_string = start.strftime('%m/%d/%Y %H:%M:%S - ')
    time_string += end.strftime('%H:%M:%S')
    return time_string
