Vigenère cipher analyzer for puzzle 04-03 of Cypher ( https://store.steampowered.com/app/746710/Cypher )

vigenere.py

import sys

key = sys.argv[1]
cipher = input()

print(f'{key = !r}')
print(f'{cipher = !r}')
print()

A = ord('A')

def o(c):
	return ord(c) - A

plain = ''

monos = [ '' for _ in key ]

for i, c in enumerate(cipher):
	k = key[i % len(key)]
	monos[i % len(key)] += c
	plain += chr((o(c) + o(k) + 1) % 26 + A)

for j, (k, mono) in enumerate(zip(key, monos)):
	print(mono, f'==[{k}]=>', plain[j:-1:len(key)])
	freq = sorted([ (l, mono.count(l)) for l in [ chr(i + ord('A')) for i in range(26) ] ], key=lambda o:o[1])
	print(*[ f'{l}-{f}' for l, f in reversed(freq) ])
	print(*[ f'{chr((o(l) + o(k) + 1) % 26 + A)}-{f}' for l, f in reversed(freq) ])
	print()

print()
print(f'{cipher = !r}')
print(f'{ plain = !r}')