Help with Coded Correspondence

Data Science
1

Hi there,

On the Data Science: Machine Learning Specialty course and I’m on the “Coded Correspondence” project. Was able to create a function to encode/decode messages, but stuck on Step 4: Solving a Caesar Cipher without knowing the shift value.
https://www.codecademy.com/journeys/data-scientist-ml/paths/dsmlcj-22-data-science-foundations/tracks/dsmlcj-22-python-fundamentals-for-data-science-part-ii/modules/dsf-python-strings-856c707b-20b8-42db-ba5f-cdf8fea8c232/projects/coded-correspondence-project

I’m trying to add a loop within the function to run 30 times and add 1 offset during each iteration.
alphabet = “abcdefghijklmnopqrstuvwxyz”
punctuation = ".,?'! "
message = “”
offset = 0
def ceaser_decode(message):
for attempts in range(0,30):
message_decoded = “”
for letter in message:
if not letter in punctuation:
letter_value = alphabet.find(letter)
message_decoded += alphabet[(letter_value + offset) % 26]
else:
message_decoded += letter
offset += 1

Get the following error when I try to call the function:
UnboundLocalError: cannot access local variable ‘offset’ where it is not associated with a value.

Can anyone help me debug, thought global variables could be accessed anywhere?

2

if you’re trying to change offset (which is a global variable since its declared outside all functions, classes, etc.)
inside a function, then you’d need to use the global statement [for that variable] in the function before the variable is changed,
so,
put
global offset
before
offset += 1
in the function.

scope for a variable can take some work to understand.

x = 5 def increase_x(): global x x += 1 increase_x() print(x)

Also, to keep your code’s formatting (such as indents), please use the </> button and put your code on lines between the ``` and ```
This would make your Python code easier to read [or run].

3

In Python, if you want to modify a global variable within a function, you need to declare it as global within the function scope using the global keyword. Try adding global offset at the beginning of your function ceaser_decode(message) to resolve the issue. This tells Python that offset refers to the global variable defined outside the function. Here’s how you can modify your function:

alphabet = "abcdefghijklmnopqrstuvwxyz"
punctuation = ".,?'! "
message = ""
offset = 0

def ceaser_decode(message):
    global offset
    for attempts in range(0, 30):
        message_decoded = ""
        for letter in message:
            if letter not in punctuation:
                letter_value = alphabet.find(letter)
                message_decoded += alphabet[(letter_value + offset) % 26]
            else:
                message_decoded += letter
        offset += 1

By adding global offset within your function, you should be able to access and modify the global variable offset within the loop without encountering the UnboundLocalError.

4

Although declaring it as a global variable fixes it, I’ve read that it’s not a good practice, ideally you have that type of variable contained within the function (local).