Hi Pythonistas!
This is part 2 of the series. If you are new, you can check part 1 here.
Today we are going to discuss "is vs ==". In Python, sometimes we use is and == operators interchangeably. It will work at times, but not always. Let me explain this with an example.
Before getting into the topic, we all should know something about a Python object. Every Python object has two things in common:
- First, its memory reference - Memory id can be found using the id function.
- Second, its value
What does ‘is’ operator do:
The is operator checks whether two objects are pointing to the same memory location.
What does ‘==’ operartor do:
The == operator checks if the value of the operator is the same.
>>> a = [1, 2, 3]
>>> b = [1, 2, 3]
>>> a == b
True
>>> a is b
False
>>> id(a)
140281424436160
>>> id(b)
140281424966208Here in this example, we can see that contents of a and b are same, but the is operator returns false and == returns true.
>>> a = [1,2,3]
>>> b = a
>>> a == b
True
>>> a is b
True
>>> id(a)
140281424966208
>>> id(b)
140281424966208
>>>Here in this example, both is and == return the same result as both of them are pointing to the same memory location.
Note: For small common strings and integers in the range -5 to 256 the memory location will be the same. Python does this for optimization. This is a big topic that can be discussed later on in an article.
What is the solution:
If you are checking equality, then always use the == operator. Use is operator only when you are checking if an object is the same as another like a is None.
happy coding !!