main.py

#!/bin/python3
from pygal import Bar
from frequency import english

# Set up data structures 
alphabet = list(' abcdefghijklmnopqrstuvwxyz ')  # List from a string
code = {}


# Create the atbash code by reversing the alphabet
def create_code():
    backwards = list(reversed(alphabet))  # Reverses a list

    for i in range(len(alphabet)):  # Gets the length of a list
        code[alphabet[i]] = backwards[
            i]  # Populate the code dictionary with a letter of the alphabet and its encoded letter

    # print(code)


# Calculate the frequency of all letters in a piece of text
def frequency(text):
    text = list(text.lower())  # Convert the message to lower case and make it a list

    freq = {}  # Create a dictionary of every letter, with a count of 0
    for letter in alphabet:
        freq[letter] = 0

    total_letters = len(text)  # Count the letters in the message

    for letter in text:
        if letter in freq:
            freq[letter] += 1

    for letter in freq:
        freq[letter] = freq[letter] / total_letters * 100  # Convert from counts to percentages

    return freq


# Make frequency chart
def make_chart(text, language):
    chart = Bar(width=800, height=400, title='Frequency analysis', x_labels=list(text.keys()))
    chart.add('Target message', list(text.values()))  # Label the frequency data for the encoded message
    chart.add('Language', list(language.values()))  # Label the frequency data for the language

    chart.render()


# Encode/decode a piece of text — atbash is symetrical
def atbash(text):
    text = text.lower()  #  Converts text to lower case
    output = ''

    for letter in text:
        if letter in code:
            output += code[letter]  # Populates output with the encoded/decoded message using the dictionary

    return output  # Return the encoded/decoded message


# Fetch and return text from a file
def get_text(filename):
    with open(filename) as f:
        text = f.read().replace('\n', '')  # Need to strip the newline characters

    return text


# Create a text-based menu system
def menu():
    choice = ''  # Start with a wrong answer for choice.

    while choice != 'c' and choice != 'f':  # Keep asking the user for the right answer
        choice = input('Please enter c to encode/decode text, or f to perform frequency analysis: ')

    if choice == 'c':
        print('Running your message through the cypher…')
        message = get_text('input.txt')  # Take input from a file
        code = atbash(message)
        print(code)

    elif choice == 'f':
        print('Analysing message…')
        message = get_text('input.txt')
        message_freq = frequency(message)
        # print(message_freq)
        lang_freq = english  # Import the English frequency dictionary
        make_chart(message_freq, lang_freq)  # Call the function to make a chart


# Start up
def main():
    create_code()
    # print(atbash('Test'))
    menu()


main()