def get_datetime(strings: Sequence[str],
                 prefix: str,
                 datetime_format_string: str,
                 ignoreleadingcolon: bool = False,
                 precedingline: str = "") -> Optional[datetime.datetime]:
    """
    Fetches a ``datetime.datetime`` parameter via :func:`get_string`.
    """
    x = get_string(strings, prefix, ignoreleadingcolon=ignoreleadingcolon,
                   precedingline=precedingline)
    if len(x) == 0:
        return None
    # For the format strings you can pass to datetime.datetime.strptime, see
    # http://docs.python.org/library/datetime.html
    # A typical one is "%d-%b-%Y (%H:%M:%S)"
    d = datetime.datetime.strptime(x, datetime_format_string)
    return d