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Python Object-Oriented Python Advanced Objects Multiplication

Han Li
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Han Li
Python Web Development Techdegree Graduate 14,817 Points

__imul__ magic method

Hi,

I have a question about imul magic method.

five = NumString("5")
original_five = five

five += 10
print(type(original_five) == type(five))

The above code snippet prints "False" to console. I think, it should be "True".

Could you explain about this problem?

Thanks, Ross

numstring.py
class NumString:
    def __init__(self, value):
        self.value = str(value)

    def __str__(self):
         return self.value

    def __int__(self):
        return int(self.value)

    def __float__(self):
        return float(self.value)

    def __add__(self, other):
        if '.' in self.value:
            return float(self) + other
        return int(self) + other

    def __radd__(self, other):
        return self + other

    def __iadd__(self, other):
        self.value = self + other
        return self.value

1 Answer

Steven Parker
Steven Parker
228,991 Points

It seems to be working properly, though "__imul__" in not involved (and not defined in the code).

When you add 10 to 5, you get 15. Since 5 is not equal to 15, the result is "False".

Han Li
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.a{fill-rule:evenodd;}techdegree seal-36
Han Li
Python Web Development Techdegree Graduate 14,817 Points

Hi Steven, Thanks for your answer.

You are right and I made a mistake for asking the question.

Here is the question I wanted.

original_five's type is "NumString". five's type is "int".

I want to make five's type "NumString".

Could you explain about this?

Thanks, Ross

Steven Parker
Steven Parker
228,991 Points

The "magic" methods all return numbers when you perform math on a NumString. But you could modify it so it returns itself and stays a NumString when you increment it. For example:

    def __iadd__(self, other):
        self.value = str(self + other)
        return self