Parse and return the default value for a datetime property.

def _parse_datetime_default_value(property_name, default_value_string):
    """Parse and return the default value for a datetime property."""
    # OrientDB doesn't use ISO-8601 datetime format, so we have to parse it manually
    # and then turn it into a python datetime object. strptime() will raise an exception
    # if the provided value cannot be parsed correctly.
    parsed_value = time.strptime(default_value_string, ORIENTDB_DATETIME_FORMAT)
    return datetime.datetime(
        parsed_value.tm_year, parsed_value.tm_mon, parsed_value.tm_mday,
        parsed_value.tm_hour, parsed_value.tm_min, parsed_value.tm_sec, 0, None)