Formats a timestamp in the format used by HTTP.

    The argument may be a numeric timestamp as returned by `time.time`,
    a time tuple as returned by `time.gmtime`, or a `datetime.datetime`
    object.

    >>> format_timestamp(1359312200)
    'Sun, 27 Jan 2013 18:43:20 GMT'

def format_timestamp(
    ts: Union[int, float, tuple, time.struct_time, datetime.datetime]
) -> str:
    """Formats a timestamp in the format used by HTTP.

    The argument may be a numeric timestamp as returned by `time.time`,
    a time tuple as returned by `time.gmtime`, or a `datetime.datetime`
    object.

    >>> format_timestamp(1359312200)
    'Sun, 27 Jan 2013 18:43:20 GMT'
    """
    if isinstance(ts, (int, float)):
        time_num = ts
    elif isinstance(ts, (tuple, time.struct_time)):
        time_num = calendar.timegm(ts)
    elif isinstance(ts, datetime.datetime):
        time_num = calendar.timegm(ts.utctimetuple())
    else:
        raise TypeError("unknown timestamp type: %r" % ts)
    return email.utils.formatdate(time_num, usegmt=True)