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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
Posted by 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
231,275 Points
Steven Parker
Steven Parker
231,275 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
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Han Li
Python Web Development Techdegree Graduate 14,817 Points
Han Li
.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
231,275 Points
Steven Parker
Steven Parker
231,275 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