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Python Object-Oriented Python Advanced Objects Multiplication

Posted by Igor Dias
Igor Dias
5,155 Points

What's the difference between multiply self or self.value inside the method?

Inside the rmul() method when I multiply other only by self it returns a numerical multiplication. On the order hand, if I multiply other by self.value it returns string multiplication. Whats the difference between the cases?

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

    def __mul__(self, other):
        if '.' in self.value:
            return float(self) * other
        return int(self.value) * other

    def __rmul__(self, other):
        return self * other

#    def __rmul__(self, other):
#        if '.' in self.value or '.' in other:
#            return float(self) * other
#        return int(self) * other

1 Answer

Steven Parker
Steven Parker
243,199 Points
Steven Parker
Steven Parker
243,199 Points

The internal value is stored as a string; but when you refer to the object itself, the internal conversion method is implicitly invoked for you to make it a number.

Igor Dias
Igor Dias
5,155 Points

Thank you, Parker!

Would you mind explaining me a little more?

This internal conversion method that you refer is the __ int _() method or the _ float __() method? Or another one? Because when I pass a string as argument the multiplication returns an int. Why not a float?

Steven Parker
Steven Parker
243,199 Points
Steven Parker
Steven Parker
243,199 Points

It gets converted based on the contents, and what you multiply it with. Try passing it a value with a decimal point.