Help understanding this code please

Could anyone please explain line by line how this code works. I know its a task on its own. But i really want to understand it. I have gone line by line myself but i get lost. Can you explain how it works and also give me an example. I would appreciate it sooooo much!!

def decode(message_file):
    #Read the contents of the file
    with open(message_file, 'r') as file:
        lines = file.readlines()

    # Extracting the number and corresponding word from each line
    number_word_pairs = {int(line.split()[0]): line.split()[1] for line in lines}

    # Building the pyramid structure
    numbers = set()
    current_line = 1
    current_num = 1

    while current_num <= max(number_word_pairs.keys()):
        if current_num == current_line * (current_line + 1) // 2:
            numbers.add(current_num)
            current_line += 1
        current_num += 1

    # Constructing the decoded message
    decoded_message = ' '.join([number_word_pairs[num] for num in sorted(numbers) if num in number_word_pairs])

    return decoded_message


# Example usage
decoded_message = decode('message_file.txt')
print(decoded_message)

I made a copy of this at:

https://replit.com/@barrycarter/ConventionalMeanDefinition#message_file.txt

but it looks like message_file.txt needs to be in a special format. Could you give us a sample message_file.txt or show us what problem you’re trying to solve?

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You can ask AI for this, but I can still try to give you some explanation line by line.

Concluding the function, it decodes an encrypted message that includes decoy values
It can raise an error upon a small criteria of conditions due to incorrect encryption or tamper, however, it is more like a format check than a tamper prevention, it might be a bug, or a feature.

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Not really, it’s just that it can be optimised.
It is not complex, not at all (compared to my “easy basic” projects it’s not complex at all)
Here is my optimised (not really) version:

def decode(message_file):
    #Read the contents of the file
    with open(message_file, 'r') as file:
        lines = file.readlines()

    # Extracting the number and corresponding word from each line
    number_word_pairs = {}
    for line in lines:
      try:
        number_word_pairs[int(line.split()[0])] = line.split()[1]
      except:
        continue

    # Building the pyramid structure
    numbers = set()
    current_line = 1
    line_idx_sum = 0
    for current_num in range(1, max(number_word_pairs.keys())+1):
        if current_num == line_idx_sum:
            numbers.append(current_num)
            current_line += 1
            line_idx_sum += current_line

    # Constructing the decoded message
    decoded_message = ' '.join([number_word_pairs[num] for num in numbers if num in number_word_pairs])

    return decoded_message


# Example usage
decoded_message = decode('message_file.txt')
print(decoded_message)
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The code I wrote there is untested and no code intelligence is used during my writing (I wrote that manually on replit ask reply draft) so I may need some time to test it rn
——————————
It seemed that I wrote ‘line_idx_sum’ to be 0 instead of 1 which made the test condition to be idx==0 at every test case which idx>0, here is a fixed version with the commented/explained encode function as well (need to provide word dictionary additionally)

import random as r

def encode(message_file, dict_file, message, min_decoy=0):
    ''' 
        message_file <- file to write the encoded message in
        dict_file <- file that include decoy word list
        message <- message to be encoded
        min_decoy <- minimum amount of decoys to be included in the output file
    '''
    message = message.split() #split the message by space
    with open(dict_file, 'r') as f: #open dict file
        words = []
        for n in f.readlines(): #read file
            if '\n' in n: #remove newline if present
                n = n[:-1]
            n = n.split()
            if not n: #if the word is empty, skip
                 continue
            n = n[0]
            if n: #if the first word is not empty
              words.append(n) #add it to the dictionary list
    if not words: #if dictionary list is empty
        print('dictionary file given contains no usable word, please provide a dictionary with word on every line for decoys in message file')
    r.shuffle(words) #shuffle the list so that the order is random
    MaxWord = 0
    for idx in range(1, len(message)+1):
        MaxWord = (1+idx)*idx//2 #add triangle structure index
        message.insert(idx-1, [str(MaxWord), message.pop(idx-1)]) #to each word
    r.shuffle(message)
    if MaxWord-len(message) < min_decoy:#if the decoy amount if not enough
        Max = len(message)+min_decoy #add more
        endDecoy = r.randint(0, MaxWord) #use some “feature” from the decode module to add some more confusing decoys
    else: #set values to init value if decoy amount is enough
        Max = MaxWord
        endDecoy = 0
    for idx in range(1, Max-endDecoy+1):
        if not words: #if dictionary is empty forget about decoys (no decoys available anyways)
            break
        for test in range(1, idx+1):
            if idx == (1+test)*test//2: #test if the index will overwrite the original message
                break #if so, bye
        else: #if still not bye
            message.append([idx, r.choice(words)]) #add decoy to message
    r.shuffle(message) #shuffle it one last time
    for idx in range(1, endDecoy+1):
        if not words: #if no dictionary then skip
            break
        message.insert(0, [r.randint(1, MaxWord), r.choice(words)]) #insert decoys in the front regardless the index, it won’t overwrite the message anyways
    with open(message_file, 'w') as f:
        for n in message:
            f.write(f'{n[0]} {n[1]}\n') #write them to the file
    
    

def decode(message_file):
        #Read the contents of the file
        with open(message_file, 'r') as file:
            lines = file.readlines()

        # Extracting the number and corresponding word from each line
        number_word_pairs = {}
        for line in lines:
            try:
                number_word_pairs[int(line.split()[0])] = line.split()[1]
            except:
                continue


        # Building the pyramid structure
        numbers = []
        current_line = 1
        line_idx_sum = 1
        for current_num in range(1, max(number_word_pairs.keys())+1):
            if current_num == line_idx_sum:
                    numbers.append(current_num)
                    current_line += 1
                    line_idx_sum += current_line

    # Constructing the decoded message
        decoded_message = ' '.join([number_word_pairs[num] for num in numbers if num in number_word_pairs])

        return decoded_message


# Example usage
encode('message_file.txt', 'dict', 'I love computer')
decoded_message = decode('message_file.txt')
print(decoded_message)
3 Likes

Thank you for taking the time to do this. Also really helpful you explained a lot. But it seems this code is a lot longer, is it still simpler than the original I posted?

Oh the reason that it is longer is that I changed the number_word_pair declaration from one line to six using try except, this way if the first word in each line isn’t a number the program won’t raise an error and stop the entire decode process

It depends whether it is simpler or not

  • In the number_word_pair declaration it is more complex to avoid error raise upon invalid syntax
  • In the while → for loop it’s performance and readability is increased by a tiny bit
  • In the line_idx_sum it increased a bit of the performance as there is no more multiplication/division/complex calculation for each loop, only addition and direct comparison. But it became harder to be identified as a triangle structure, rather a jump in numbers (sum)
  • in the “construct decode message” line it is shortened so technically simpler?

For the encode function I wrote yeah it’s a bit of a mess due to my bad habit of naming variables with only 1 letter

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