I was in my computer science class today and the teacher put a piece of python coding on the board and said he couldn't figure out why it wasn't working. He was showing us functions and said:

```
def app(x):
    x.append(" ")
    print(x)

def ext(x,y):
    x.extend(y)
    print(y)

nums = [1,2,3,4,5,6]
numbers = [7,8,9,10]

app(nums)
ext(nums,numbers)

print("End of program")

```

The code was meant to show how when you don't type

```
return x

```

in the function then the variable doesn't change when you return to the main program however when he ran the program, the first function added the space and kept it there when it returned resulting in the following text being printed...

```
['1','2','3','4','5','6',' ']
['1','2','3','4','5','6',' ','7','8','9','10']
End of program

```

Please help me out.