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Python Basic Object-Oriented Python Emulating Built-ins __eq__

__eq__ why do we need it?

If python can already do this, why do we need this dunder eq? Could someone explain please, thanks!

list1 = [2, 3]
list2 = [2, 3]
if list1 == list2:
    print("eq")
else:
    print("not eq")
eq

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 67,778 Points

Hey Riley Ittidecharchoti, great question!

The built-in types, such as list, all have __eq__ defined. Any new class that is derived from the built-in types will inherit the __eq__ method.

If a new class is defined that does not inherit from a built-in type and it will be used in a == comparison statement, then it must have an __eq__ method defined or it can not be compared. In other words, the == operator calls the __eq__ method.

Post back if you need more help. Good luck!!!

Thank you! I get it. Thanks for taking the time to reply. The same for the other dunder ones ( what should I refer to them as ) right?

Chris Freeman
Chris Freeman
Treehouse Moderator 67,778 Points

Correct! Each of the dunder or “special named” methods, have a one-to-one correspondence to using an operator on the object, the object being callable, using the object as hashable type in a dictionary key, etc. Basically a dunder method for every context an object might be used in.