reversing a string

[kerzol81]

Hello,

I was given a homework, the output should look like this:

W
Wo
Wor
Worl
World
World
World H
World He
World Hel
World Hell
World Hello

The teacher suggested this solution:

userInput = 'Hello World'

userInput = userInput.split(' ')

userInput = userInput[::-1]

userInput = ' '.join(userInput)

tmp = ''

for char in userInput:
    tmp += char
    print(tmp)

I dont understand why we need an additional tmp variable. Could someone please explain it to me, or have a better, more pythonic solution?