Python function that uses a word as the encryption key, rather than an integer

[perfringo]

Reading this code I get little bit confused.

- why you import alphabet_position and then define function with same name?
- why you ask two times for letter?
- is it typo or functions rotate is not indented?

Instead of writing dictionary manually one can let Python create it:

alphabet_pos = {}

for i, v in enumerate(zip(range(65, 91), range(97, 123))):
    alphabet_pos.update({**dict.fromkeys([chr(v[0]), chr(v[1])], i)})

It is also not clear what function vigenere_cipher should accomplish.