Convert datetime.datetime time to UTC

    If value doesn't have tzinfo, then defaulttz is set.
    Default value of defaulttz is local time zone.

def to_utc(value, defaulttz=None):
    """Convert datetime.datetime time to UTC

    If value doesn't have tzinfo, then defaulttz is set.
    Default value of defaulttz is local time zone.
    """
    if defaulttz is None:
        defaulttz = tzlocal()
    return _convert(value, tzutc(), defaulttz)