Best practice in python for return value on error vs. success

Question

In general, let\'s say you have a method like the below.

def intersect_two_lists(self, list1, list2):
    if not list1:
        self.trap_e         


        

Answer 1

It'd be better to raise an exception than return a special value. This is exactly what exceptions were designed for, to replace error codes with a more robust and structured error-handling mechanism.

class IntersectException(Exception):
    def __init__(self, msg):
        self.msg = msg
    def __str__(self):
        return self.msg

def intersect_two_lists(self, list1, list2):
    if not list1: raise IntersectException("list1 must not be empty.")
    if not list2: raise IntersectException("list2 must not be empty.")

    #http://bytes.com/topic/python/answers/19083-standard
    return filter(lambda x:x in list1,list2)

In this specific case though I'd probably just drop the tests. There's nothing wrong with intersecting empty lists, really. Also lambda is sort of discouraged these days in preference to list comprehensions. See Find intersection of two lists? for a couple of ways to write this without using lambda.