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Python Object-Oriented Python Advanced Objects Multiplication

Posted by chen liu
chen liu
3,188 Points

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

Why using "float(self)" and "float(self.value)" both work? I could not understand using "self".

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.value) * other
        return int(self.value) * other

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

1 Answer

dublinruncommutr
dublinruncommutr
5,944 Points
dublinruncommutr
dublinruncommutr
5,944 Points

self.value is a string. So when you call float(self.value) you are calling the __float__ method for a str object

When you call float(self) you are calling self.__float__() which you have defined as returning float(self.value) which then returns the __float__ method for the str object representing your number.

self is an instance of NumString. Try adding a printTypes() function to see what is happening here and it will make more sense.

def printTypes(self):
        print("Here is what self is: {}. Here is what self.value is {}".format(type(self), type(self.value)))