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Question

This is a question of python challenge which I am not able to answer:

class wow:
def__init__(s,x):
s.x = x
def__add__(s,y):
return wow(s.y - y.x)
def__sub__(s,y):
return wow(s.x + y.x)
def__repr__(s):
return str(s.x)

a = wow(5)
b = wow(7)
c = wow(3)
print(a-b+c)

Please, help me to know the solution
Thanks for your solutions !

Answer 1

Let's go through this step by step:

a = wow(5)
What this step does is to create an instance of the class called "a" with an "x" value of 5.

b = wow(7)
Similarly, another instance is created with an "x" value of 7.

c = wow(3)
Same thing.

print (a-b+c)
What is a-b? This is not defined usually (you can't just subtract instances of classes) but as the "-" operator is overloaded in the class, this is instead defined by the user. Take a look at this line:

def __sub__(s, y):
return wow(s.x - y.x)

Rather misleadingly, this line says that when "adding" instances of classes together, subtract their "x" value by the other instance's "x" value. Hence, a-b = a's "x" value + b's "x" value = 12.

Similarly for "+", the plus operator now subtracts the second "x" value from the first "x" value, hence (a-b) (which has an "x" value of 12) - c = 9.

Hence, the answer is 9.
(BTW, the __repr__ is used to return a printable representation of the object.)

Answer 2

This effect was treaten in python course as "magic words" .
it was not ment kidding python learners.

The usual usecase for that is to use common operators for all objects if wanted.

Anyhow this challenge opened my eyes.

Answer 3

@ blackcat1111
Thanks for giving me such a wonderful explanation !

Answer 4

Welcome! 🙂

Answer 5

__add__ overrides + operator of wow objects
__sub__ overrides - operator of wow objects
__mul__ overrides * operator of wow objects.
And so on.
Hence they profuce a different value with the initialized values due to the altered operators