== vs is

Every thing in Python is an object. Variables are nothing but pointers to those objects. Therefore, multiple variables can point to the same object. Therefore:

• To test whether two variables point to the same object, we use is operator which compares the identity of both variables. If the return value is True -> both variables point to the same object. This can also be tested in CPython using id().
• To test if both variables (objects they point to) have the same content, we use == operator.

a = [2]
b = a
a is b          #=> True
id(a) == id(b)  #=> True


a = [2]
b = [2]
a is b          #=> False
id(a) == id(b)  #=> True

It is recommended to use is operator when checking if a variable is: True, False, or None. If we use ==, it will invoke __eq__ method, which if not implemented, compare the ids of both variables and is slower than is operator because it first has to look up __eq__ method and then invoke id() on both variables.