When Do `is` and `==` Operators Return Different Results in Python?

Understanding the "is" Operator

Despite having the same values, when using the "is" operator, a common misconception is to assume it compares the variable values. However, this operator actually evaluates whether two variables refer to the same object.

In your example, the following code:

x = [1, 2, 3]
y = [1, 2, 3]

may lead you to expect the "is" operator to return True, but it returns False:

print(x is y)  # False

This is because x and y, despite sharing the same values, are considered two distinct lists. They are different objects, as revealed by their unique identifiers:

print(id(x))
print(id(y))  # Different identifiers indicate different objects

To compare values, use the "==" operator instead:

print(x == y)  # True for equal values

Modifying one of the lists will not affect the other, confirming they are separate objects:

x[0] = 4
print(y)  # [1, 2, 3] (Unchanged)

Assigning y to x creates a new reference pointing to the same list object:

x = y
print(id(x))
print(id(y))  # Same identifiers after assignment
print(x is y)  # True (Same object)

Remember, the "is" operator tests object identity, while the "==" operator compares values. Use them judiciously to avoid potential confusion in understanding variable referencing behavior.

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