How to creat a function that receives a tuple of characters and returns them in an organised form so I can use it as a key generator

[pedrorenato1998 at gmail.com]

Hello guys. so my assignment consists in creating a key generator so i can use it in later steps of my work. In my first step i have to write a function called key_generator that receives an argument, letters, that consists in a tuple of 25 caracters. The function returns a tuple of 5 tuples of caracters, each tuple with 5 elements. 
 Sounds confusing right? well I have the final product but i dont know how to get there. I was told by my professor that I dont really have to use any complicated knowledge of python so I have to keep it simple. 
I've tried so many times to reproduce a code that does that but i just cant do it! When i google it i only find complicated python concepts that i didnt even studied in class. Can u help me plz? just give me a hint how to do it and i'll do everything plz. 

example: 
Python Shell 

>>> letters = (‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’, ‘G’, \ 
... ‘H’, ‘I’, ‘J’, ‘ ’, ‘L’, ‘M’, ‘N’, \ 
... ‘O’, ‘P’, ‘Q’, ‘R’, ‘S’, ‘T’, ‘U’, \ 
... ‘V’, ‘X’, ‘Z’, ‘.’) 
>>> key_generator(letters) 
... ((‘A’, ‘B’, ‘C’, ‘D’, ‘E’), 
... (‘F’, ‘G’, ‘H’, ‘I’, ‘J’), 
... (‘ ’, ‘L’, ‘M’, ‘N’, ‘O’), 
... (‘P’, ‘Q’, ‘R’, ‘S’, ‘T’), 
... (‘U’, ‘V’, ‘X’, ‘Z’, ‘.’))