Question

class x:
    def __init__(self,name):
        self.name=name

    def __str__(self):
        return self.name

    def __cmp__(self,other):
        print("cmp method called with self="+str(self)+",other="+str(other))
        return self.name==other.name
       # return False


instance1=x("hello")
instance2=x("there")

print(instance1==instance2)
print(instance1.name==instance2.name)

The output here is:

cmp method called with self=hello,other=there
True
False

Which is not what I expected: I’m trying to say ‘two instances are equal if the name fields are equal’.

If I simply return False from the __cmp__ function, this reports as True as well!!
If I return -1, then I get False – but since I’m trying to compare strings, this doesn’t feel right.

What am I doing wrong here?

Answer 1

__cmp__(x,y) should return a negative number (e.g. -1) if x < y, a positive number (e.g. 1) if x > y and 0 if x == y. You should never return a boolean with it.

What you’re overloading is __eq__(x, y).