#### Polybius

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```#!/usr/bin/env python3

"""
A Polybius Square is a table that allows someone to translate letters into numbers.

https://www.braingle.com/brainteasers/codes/polybius.php
"""

import numpy as np

SQUARE = [
["a", "b", "c", "d", "e"],
["f", "g", "h", "i", "k"],
["l", "m", "n", "o", "p"],
["q", "r", "s", "t", "u"],
["v", "w", "x", "y", "z"],
]

class PolybiusCipher:
def __init__(self) -> None:
self.SQUARE = np.array(SQUARE)

def letter_to_numbers(self, letter: str) -> np.ndarray:
"""
Return the pair of numbers that represents the given letter in the
polybius square
>>> np.array_equal(PolybiusCipher().letter_to_numbers('a'), [1,1])
True

>>> np.array_equal(PolybiusCipher().letter_to_numbers('u'), [4,5])
True
"""
index1, index2 = np.where(letter == self.SQUARE)
indexes = np.concatenate([index1 + 1, index2 + 1])
return indexes

def numbers_to_letter(self, index1: int, index2: int) -> str:
"""
Return the letter corresponding to the position [index1, index2] in
the polybius square

>>> PolybiusCipher().numbers_to_letter(4, 5) == "u"
True

>>> PolybiusCipher().numbers_to_letter(1, 1) == "a"
True
"""
return self.SQUARE[index1 - 1, index2 - 1]

def encode(self, message: str) -> str:
"""
Return the encoded version of message according to the polybius cipher

>>> PolybiusCipher().encode("test message") == "44154344 32154343112215"
True

>>> PolybiusCipher().encode("Test Message") == "44154344 32154343112215"
True
"""
message = message.lower()
message = message.replace("j", "i")

encoded_message = ""
for letter_index in range(len(message)):
if message[letter_index] != " ":
numbers = self.letter_to_numbers(message[letter_index])
encoded_message = encoded_message + str(numbers[0]) + str(numbers[1])
elif message[letter_index] == " ":
encoded_message = encoded_message + " "

return encoded_message

def decode(self, message: str) -> str:
"""
Return the decoded version of message according to the polybius cipher

>>> PolybiusCipher().decode("44154344 32154343112215") == "test message"
True

>>> PolybiusCipher().decode("4415434432154343112215") == "testmessage"
True
"""
message = message.replace(" ", "  ")
decoded_message = ""
for numbers_index in range(int(len(message) / 2)):
if message[numbers_index * 2] != " ":
index1 = message[numbers_index * 2]
index2 = message[numbers_index * 2 + 1]

letter = self.numbers_to_letter(int(index1), int(index2))
decoded_message = decoded_message + letter
elif message[numbers_index * 2] == " ":
decoded_message = decoded_message + " "

return decoded_message
```