The return is indented inside of the if statement so it will return straight away.
The return needs to be indented level with the for statement, it then will loop through all the letters before it returns the list.
It would also be a good idea to move the definition lista = [] into the start of the function.
The return needs to be indented level with the for statement, it then will loop through all the letters before it returns the list.
It would also be a good idea to move the definition lista = [] into the start of the function.