Question

When implementing a custom equality function for a class, does it make sense to check for identity first? An example:

def __eq__(self, other):
    return (self is other) or (other criteria)

This interesting is for cases when the other criteria may be more expensive (e.g. comparing some long strings).

Answer 1

necesarry: no

does it make sense: sure, why not?

No such check is done by default, as you can see here:

class bad(object):
    def __eq__(self, other):
        return False

x = bad()
print x is x, x==x # True, False