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Python Object-Oriented Python Advanced Objects Frustration

Posted by Juan Suarez
Juan Suarez
1,406 Points

frustration.py

class Liar(list):

def doublelenght(self):
    return '{}{}'.format(self,self)

def __len__(self):
    return len(self.doublelenght())

bad_list = Liar([1,1])

print(bad_list) print(bad_list.doublelenght()) print(len(bad_list))

12

my idea was doubling the list and so the result I expected based on [1,1] was 4 but inseard instead is giving me 12, not sure the why this is happening.

frustration.py
Jura Streaming
Jura Streaming
8,082 Points
Jura Streaming
Jura Streaming
8,082 Points

Hi! The len() is not 4 because it is counting characters inside string type of variable returned by doublelenght(), and there is 12 characters there

>>> print(bad_list.doublelenght())
[1, 1][1, 1]
>>> type(bad_list.doublelenght())
<type 'str'>
>>> len("[1, 1][1, 1]")
12
>>>

In your case, if I correctly understood what you drive to create, you need to expand list like so:

class Liar(list):
    def doublelenght(self):
        return self + self

    def __len__(self):
        return len(self.doublelenght())

and the test of it:

>>> bad_list = Liar([1,1])
>>> len(bad_list)
4
>>> bad_list.doublelenght()
[1, 1, 1, 1]
>>> len(bad_list.doublelenght())
4
>>>

2 Answers

Avery Uslaner
Avery Uslaner
15,099 Points
Avery Uslaner
Avery Uslaner
15,099 Points

So your method doubleleght[sic] is just printing out the list twice. So it's returning:

[1, 1][1, 1]

And your len method is just counting those characters. And as you can see, there are 12 characters so that's why you're getting 12. To get your intended result, try something like:

def doublelength(self):
    return len(self) * 2

That way you don't even need to bother overriding the len method.

Juan Suarez
Juan Suarez
1,406 Points
Juan Suarez
Juan Suarez
1,406 Points

got it thanks guys!!