Python's Magic Methods in Classes (Summary)

For me, the biggest take away is the understanding of ‘init()’ and the ‘str()’ dunder methods.

I created the Storage class without saving the ‘value’ attribute in the instance since it should have been created by the super().__new__(class, value).

class Storage(float):
    def __new__(cls, value, unit):
        instance = super().__new__(cls, value)
        instance.unit = unit
        return instance
    def __str__(self):
        return f'{super().__repr__()} {self.unit}'

When I created the object >>> storage_size = Storage(512, 'GB'), entering just storage_size in the repl, the value ‘512’ was printed out. So the value was available from the object. Using the print() function, the output was 5120 GB as per the __str__ method.

When I tried to create the __repr__ method in a similar fashion, I got a recursion error. With my modified class object, how do I get the underlying float value from the inherited class from the __repr__ method’s ‘self’ object. I thought that including an instance.value attribute was essentially duplicating the underlying float value provided by the inherited class.

Great course, Negar!! I like how you introduced and explained things. I have used some of these magic methods in the past, but will be using them more in the future. I look forward to more courses from you!

@bhchurch6 I did the same implementation and added a comment to that chapter of the course, not yet having seen your comment above.

“I thought that including an instance.value attribute was essentially duplicating the underlying float value provided by the inherited class.” - I fully agree.

I also ran into the recursion error and posted this on SO. Hope it helps.