Python: Why “return” won´t print out all list elements in a simple for loop and “print” will do it?

Question

Im trying to print out all elements in a list, in Python, after I´ve appended one list to another. The problem is that it only prints out every element when I use PRINT inst

Answer 1

return means end of a function. It will only return the first element of the list.

For your print version, a.append(b) makes a = [1,2,3,4,[1,2,3]] so you will see the elements before None. And the function returns nothing, so print union(a, b) will print a None.

I think you may want:

def union(a, b):
    a.extend(b)
    return a

Or

def union(a, b):
    return a + b