1def plugboard(to_convert, list_of_letter_pairs):
 2    """Convert a given string using sets of two letters. Each letter converts to its neighbor."""
 3    converted = ''
 4    for ch in to_convert:
 5        # create a list of all sets that contain the current letter
 6        corresponding_set = [letters_set for letters_set in list_of_letter_pairs if ch in letters_set]
 7
 8        # if the list is empty or the current character
 9        # isn't a letter, then the character will not be changed
10        if not corresponding_set or not ch.isalpha():
11            converted += ch
12        else:
13            # get difference between the set {'ch', 'other_letter'} and {ch} to find 'other_letter'
14            # (next() and iter() are used to extract the single member of the set)
15            converted += next(iter(corresponding_set[0] - {ch}))
16    return converted
17
18
19def rotor(to_convert, dict_letters):
20    converted = ''
21    for ch in to_convert:
22        if not ch.isalpha():  # only convert letters
23            converted += ch
24            continue
25        converted += dict_letters[ch]
26    return converted
27
28
29def enigma_encrypt(plugboard_position=[], rotor_position={}):
30    def decorator(func):
31        def inner(to_encrypt):
32            after_plugboard = plugboard(to_encrypt, plugboard_position)
33            after_rotor = rotor(after_plugboard, rotor_position)
34            func(after_rotor)
35        return inner
36    return decorator
37
38
39def enigma_decrypt(plugboard_position=[], rotor_position={}):
40    def decorator(func):
41        def inner(to_decrypt):
42            rotor_reversed = {v: k for k, v in rotor_position.items()}
43            after_rotor = rotor(to_decrypt, rotor_reversed)
44            after_plugboard = plugboard(after_rotor, plugboard_position)
45            func(after_plugboard)
46        return inner
47    return decorator