Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

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("not eq")

1 Answer

Chris Freeman
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.