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Python Object-Oriented Python Advanced Objects Controlling Conversion

Kohei Ashida
Kohei Ashida
4,882 Points

Why is there str(value) in the first def

Kenneth has written the first def in the NumString class like

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)

but why should str(value) be put in the first def? I thought it should be like below lines.

class NumString:
    def __init__(self, value):
        self.value = value    #str() removed

    def __str__(self):
        return str(self.value)    #str() added

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

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

What are advantages in writing like Kenneth did?

2 Answers

Steven Parker
Steven Parker
231,186 Points

The purpose of the class is to store numeric values as strings. The modification in the second example would cause it to store the value as a number, but convert it into a string on demand. To complete the modification, you'd need to make changes to the other methods as well.

Technically, the functionality could be reproduced the other way, but if the main intention of the class is to hold a value as a string, only the first example accomplishes that.

Kohei Ashida
Kohei Ashida
4,882 Points

Thanks so much, Steven! I forgot that Kenneth explained that it's to store numeric values as strings as you mentioned.