Python has two versions of equality; they are == (plain equality) and is identity. Actual is identity, as in ‘a is b‘, tests whether the two things are in fact the exact same object.== can compare different types of objects and return useful results if desired. a == b checks if a and b have same value. a is b checks if a and b refer to same object.

What happen when we assign names

x = 7
 
y = x
 
x = 5

Has the value of y changed? The answer is NO, why should it? Values of type int, float, bool, str are immutable. For immutable values, we can assume that assignment makes a fresh copy of a value. Updating one value does not affect the copy.

Consider the below case:

one = [1,2,3,4,5]
 
two = one
 
one[2] = 0

This will result in the variables one and two to contain the same newly edited list.

On editing any one list in this case list one the other list two also changed because both of them points the same list [1,2,3,4,5]. one and two are two names for the same list.

For mutable values, assignment does not make a fresh copy. One other instant a correction can be applied by generating a copy of list while assigning.

one = [1,2,3,4,5]
 
two = one[::]
 
one[2] = 0

This will result in the variables one and two to contain two different list.

Here in this case on editing list one doesn’t alter the elements of list two. The variable list two is assigned a full slice of list one. A slice creates a new (sub)list from an old one. Both the variable points two different copy of lists but of same value.

Now we can easily understand what’s the digression on equality:

one = [1,2,3,4,5]
 
two = [1,2,3,4,5]
 
three = two

Here,

one == two is True two == three is True

and

two is three is True one is two is False

one is two is false because list one and two are not the same object but two different object of same value and type.