In Python, null variables are known as none. Let's create a variable and set it to none. The correct way to check for this is with the is operator. There's another way you could do it. You could do if fu=none and that works, but it's not the preferred way in Python.
Let me show you why. If I do id(fu), it gives me the ID of the variable fu, and in Python everything has an ID and a value. Whenever we use the is operator, it does an ID comparison, whereas if we use the equals, then it requires a inaudible 0:45 to look up and has to iterate through it to do the comparison. The end result is the is, is much faster than using equals when checking for none.