Why append don't work, pass by reference?

Question

I have writtern the below codes

a = [1,2,3]
b = a.append(4)

Why there is nothing inside b ?

Answer 1

Because append doesn't return the modified list - it simply adds the new element, modifying the list in-place and returning None . To get the effect you want, do this instead:

b = a + [4]

Notice that the above creates a new list, whereas using append modifies the same list.

Answer 2

I am not 100% sure what it is you want the value of b to be. But here is what it is when you run the code.

The value of b is None, because it is the return value of the method (.append()) Every method will return a value. In this case it is None, because a.append(4) is appending to the array a. Returning a value means to SIMPLY return a value. This doesn't require a value.

Answer 3

append returns None, That's why there is nothing in b. Your list a will be modified and added 4.

If you realy want to add 4 in b then you can try a + [4]