How do I use ASCII (and not Unicode) in Python?

Question

I'm trying to make a Caesar cipher encryptor/decryptor in Python, by getting the ASCII index of a letter and adding/subtracting from it. However, it seems to be using Unicode instead because I get letters with accents instead of just English alphabet letters. For example, if I enter the word 'weasel' and encrypt it by 2, what I get is 'yÞĿƲȗʃ'. How do I use ASCII?

Here is my code:

    def manipulate(text, key, e_or_d):
        ciphertext = ''
        for i in text:
            asciiCode = ord(i)
            if e_or_d == 'e':
                key = ord(i) + key
            elif e_or_d == 'd':
                key = ord(i) - key
            newChar = chr(key)
            ciphertext += newChar
        if e_or_d == 'e':
                print('Here is your encrypted text: ')
        elif e_or_d == 'd':
            print('Here is your decrypted text: ')
        print(ciphertext)
    
    text = input('Enter text: ')
    e_or_d = input('Enter \'e\' for encryption or \'d\' for decryption: ')
    key = int(input('Enter encryption key: '))
    manipulate(text, key, e_or_d)

I used chr and ord here to turn an index into a character and identify the index of a character, respectively.

Sorry if this is incoherent and disorganised.

You are accumulating on key variable that arrives to the function. Try new_ord = ord(i) + key instead of key = ord(i) + key to keep key the same throughout i.e., what user supplied. Similar goes for decryption if. — Mustafa Aydın
– Mustafa Aydın, Commented May 7, 2021 at 10:38
another thing to note is a-z only range from 97-122, so case like manipulate("weasel", 4, "e") will give you unexpected result and you need to handle it. — adamkwm
– adamkwm, Commented May 7, 2021 at 11:10
You should probably read Joel Spolsky's The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excluses!) All Python 3 strings are Unicode strings; you just have to understand how Unicode is organized. In brief, the first 128 characters are the ASCII subset. — tripleee
– tripleee, Commented May 10, 2021 at 4:59

jtlz2 · Accepted Answer · 2021-05-07 10:54:43Z

2

It is taking using ascii. You are increasing key by ord(i) for every iteration in the loop. So it is not constant. Use a new variable instead of key and it should work.

def manipulate(text, key, e_or_d):
    ciphertext = ''
    for i in text:
        asciiCode = ord(i)
        if e_or_d == 'e':
            temp = ord(i) + key
        elif e_or_d == 'd':
            temp = ord(i) - key
        newChar = chr(temp)
        ciphertext += newChar
    if e_or_d == 'e':
        print('Here is your encrypted text: ')
    elif e_or_d == 'd':
        print('Here is your decrypted text: ')
    print(ciphertext)

NOTE: I think using boolean values for e_or_d would be better. Also keep your variable names consistent, like using camel case only or using _ only.

edited May 7, 2021 at 10:54

jtlz2

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answered May 7, 2021 at 10:44

SPARTACUS5329

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Comments

adamkwm · Accepted Answer · 2021-05-08 02:30:59Z

There are few things to notice:

you are changing key in every loop while it should keep the same, so you need another variable to save result
ord(a)-ord(z) range from 97-122, you may have unexpected result even after changing point 1, for example, manipulate("a", 1, "d") is ` and manipulate("z", 1, "e") is {, as they are out of range after manipulate.

I suppose the user will only input lowercase letter, if they will input uppercase letter or other character, extra checking is needed, here's the code changing just 2 points above:

def manipulate(text, key, e_or_d):
    ciphertext = ''
    if e_or_d == "e":
        step = 1
        action = "encrypted"
    elif e_or_d == "d":
        step = -1
        action = "decrypted"
    for i in text:
        # * step means + key in encryption and - key in decryption
        new_ord = ord(i) + (key * step)
        # check if new_ord is inside the range of a-z
        if 97 <= new_ord <= 122:
            new_char = chr(new_ord)
        else:
            # if new_ord > 122, it will - 26, elif new_ord < 97, it will + 26
            new_char = chr(new_ord - (26 * step))
        ciphertext += new_char
    print(f'Here is your {action} text: ')
    print(ciphertext)

text = input('Enter text: ')
key = int(input('Enter encryption key: '))
e_or_d = input('Enter \'e\' for encryption or \'d\' for decryption: ')
manipulate(text, key, e_or_d)

Output:

Enter text: weasel
Enter encryption key: 2
Enter 'e' for encryption or 'd' for decryption: e
Here is your encrypted text:
ygcugn

Enter text: a
Enter encryption key: 1
Enter 'e' for encryption or 'd' for decryption: d
Here is your decrypted text:
z

Enter text: z
Enter encryption key: 1
Enter 'e' for encryption or 'd' for decryption: e
Here is your encrypted text:
a

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