where '%(field)s' is replaced with return value of the get_text_list function called with 2 arguments: unique_check and return value of the function six.text_type called with return value of the function _ with an argument string 'and', return the result. define the method get_date_error_message with 2 arguments: self and date_check.
def get_date_error_message ( self , date_check ) :