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Python Object-Oriented Python Advanced Objects Frustration

Matt Otis
Matt Otis
1,402 Points
Posted by Matt Otis
Matt Otis
1,402 Points

Frustration.py and Super() Value Mart

Seems like this code should work....

frustration.py 
class Liar(list):
    def __len__(self):
        actual_len = super().__len__(self)
        dummy_len = 5
        if actual_len == dummy_len:
            dummy_len += 1
        return dummy_len

But, I’m getting return of...

TypeError: expected 0 arguments, got 1

Why would it expect 0 arguments when I’m clearly trying to call a method and get a value?

Also, where am I going wrong?

2 Answers

Anthony Crespo
seal-mask
.a{fill-rule:evenodd;}techdegree
Anthony Crespo
Python Web Development Techdegree Student 12,973 Points
Anthony Crespo
.a{fill-rule:evenodd;}techdegree
Anthony Crespo
Python Web Development Techdegree Student 12,973 Points

The function __ len__ actually don't take any argument.

If you take the argument off your code it will work.

class Liar(list):
    def __len__(self):
        actual_len = super().__len__(). # don't need to pass anything here
        dummy_len = 5
        if actual_len == dummy_len:
            dummy_len += 1
        return dummy_len

I just started learning python but this is how I understand it.

Normally, when you want to call the len() function in your code you will do this:

a = [1,2,3]
len(a)

It tells to the variable "a" to call the function __ len__ and it will return the length of it. It mean you could do:

a = [1,2,3]
a.__len__()

Like you can see len() who is __ len__() don't need a variable it already knows you want to return the length of "self". 

class Liar(list):
    def __len__(self):  # this function override the __len__ function of list...
        actual_len = super().__len__(). # ...but you can still use it if you want and get the length like before you override it
        dummy_len = 5
        if actual_len == dummy_len:
            dummy_len += 1
        return dummy_len

Use self.function_name to call a function in your class and super().function_name to call one of the function your class inherited.

Matt Otis
Matt Otis
1,402 Points
Matt Otis
Matt Otis
1,402 Points

Thanks for your insight. I hadn’t quite put together that:

len(a) == a.__len__()

That and your insight about self.function_name and super().function_name was super helpful in helping me ‘get’ it.

Thanks Anthony!

fwiw this is the code that passed:

frustration.py 
class Liar(list):
    def __len__(self):
        actual_len = super().__len__()
        dummy_len = 5
        if actual_len == dummy_len:
            dummy_len += 1
        return dummy_len