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Python

Posted by ygh5254e69hy5h545uj56592yh5j94595682hy95
ygh5254e69hy5h545uj56592yh5j94595682hy95
7,934 Points

Python OOP

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

    def __str__(self):
        print('__str__ ran')
        return self.value

    def __int__(self):
        print('__int__ ran')
        return int(self.value)

    def __float__(self):
        print('__float__ ran')
        return float(self.value)

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

    def __radd__(self, other):
        print('__radd__ ran')
        return self + other

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

a = NumString('10.5').__add__(10)
print(isinstance(a, float))

# When I run the code I get:
#   __add__ ran <--- Makes sense to get this back
#   __float__ ran <--- I don't know why I got this back. I didn't call the __float__
#   True <--- Makes sense

# But when I change the value to "10"(a = NumString('10').__add__(10)), I get this back
#   __add__ ran <--- makes sense
#   __int__ ran <--- why ;/
#   False <--- makes sense

# So why did __float__ and __int__ showed up when I did not even call them?
# Is __float__ and float()  && __int__ and int() the same thing but just written differently?

1 Answer

Ronald Kratochwill
Ronald Kratochwill
11,213 Points 
# When I run the code I get:
#   __add__ ran <--- Makes sense to get this back
#   __float__ ran <--- I don't know why I got this back. I didn't call the __float__
#   True <--- Makes sense

# The output you get that says __float__ ran is because this method overrides what is called
# when float() is called. your  __add__ does call __float__ if the string has a period in it.

# But when I change the value to "10"(a = NumString('10').__add__(10)), I get this back
#   __add__ ran <--- makes sense
#   __int__ ran <--- why ;/
#   False <--- makes sense

# This is the same thing. When the number has no period in it, it changes it to 
# an int. __init__ is called by your __add__ function

# dunder functions such as __add__, __float__, and __int__ overide the functions for 
# objects created by the class they are in. __add__ overides how the + operator works,
#  __int__ overides how int() function works and __float__ changes how the float() function works

# For example, because of this when you declare the following...
a = NumString(10.5)

# You can add the NumString to a number by doing this:
answer = a + 5
ygh5254e69hy5h545uj56592yh5j94595682hy95
ygh5254e69hy5h545uj56592yh5j94595682hy95
7,934 Points

Thank you, now it makes sense!