from datetime import datetime


def json_iso_dttm_ser(obj):
    """
    json serializer that deals with dates

    >>> dttm = datetime(1970, 1, 1)
    >>> json.dumps({'dttm': dttm}, default=json_iso_dttm_ser)
    '{"dttm": "1970-01-01T00:00:00"}'
    """
    if isinstance(obj, datetime):
        obj = obj.isoformat()
    return obj