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Antoni Majewski
3,128 Pointslen() vs. __len__
Hello,
I don't understand when I should define __len__ here, and not just len() - what's the difference?
Thanks~!
2 Answers
Chris Freeman
Treehouse Moderator 68,457 PointsGood question. The function len() is a built-in function in python and should not be user defined. The proper way to get the length of an object is to call the built-in function with the object as the argument: len(obj)
The built-in len() will call the object’s __len__ method. So it is the __len__ method that should be defined.
Post back if you need more help. Good luck!!!
Izabella Exeoulitze
Courses Plus Student 1,665 PointsThank you Chris!
Izabella Exeoulitze
Courses Plus Student 1,665 PointsIzabella Exeoulitze
Courses Plus Student 1,665 PointsChris, thanks for the answer. I have a clarification question for you: are you saying that we cant modify/define len() but everything that has dunder is 'modifiable'? Much appreciate all your help. Isabella
Chris Freeman
Treehouse Moderator 68,457 PointsChris Freeman
Treehouse Moderator 68,457 PointsIzabella Exeoulitze, yes, the dunder methods are how an class responds to a call by the built in functions. Those can be modified and overridden as needed. The built in functions should not be modified.
Chris Freeman
Treehouse Moderator 68,457 PointsChris Freeman
Treehouse Moderator 68,457 PointsFor those that asked, if you are defining a class that does not inherit from a built-in type, will not inherit a
__len__method. So if you wish to use len() on this class the__len__method will need to be defined.