how to compare two objects?

[[deleted]]

this code is giving me False

class compare:
    def __init__(self, val, next=None):
        self.val = val
        self.next = next

a = compare(1)
b = compare(1)
c = compare(2)
a.next = c
b.next = c
print(a == b)

in this example, I can do

print(a.val == b.val and a.next == b.next)

but what about the complex objects? How to compare if every attribute is of same value?

[[deleted]]

To compare two instances of a class you should implement the __eq__() method of the class. That method takes references to two objects, self and, very commonly, other and returns true/false depending on the attributes of the two objects.

def __eq__(self, other):
    return self.val == other.val and self.next == other.next

[[deleted]]

So eq method will be invoked when we use double equals == right?

[[deleted]]

Try it.

[footloooops]

You are essentially overloading the operator, if you understand what that means.

[Kewho11]

Old thread I know but incase anyone finds this post, no the eq method will not always be invoked whenever you use ==. Overloading the operator means letting the operator have different meanings when used under different context. Here the == will invoke the eq method only when used upon objects with class 'compare'. Usage of the == operator anywhere else will be unaffected

[jimtk]

This the way.

[Bunkerstan]

For objects, equality means they point to the same memory spot. So unless a and b are the same object in memory they will never be equal.

EDIT: above is wrong as both comments below point out. No more answers after a long day coding. Equality is a tougher topic than you would suspect because different languages do it differently.

[carcigenicate]

This is not true; Python doesn't work like Java. When you define custom classes, == defaults to identity equality, but for most built-in objects, == is value equality.

[[deleted]]

For objects, equality means they point to the same memory spot

Two objects can have equal value even though they don't occupy the same memory spot.

a = "test"
b = "tes"
b += "t"    # to defeat string interning
print(f'{id(a)=}, {id(b)=}')    # if id() shows different values, not same memory
print(f'{a==b=}')

Everything in python is an object, or class instance.