Python error question!

I’m doing an assignment for the 1 week course 2. In the UNQ_C6 replace_letter function, I have an error code as follows.

replace_set = {word[:i] + c + word[i+1:] for i in range(len(word)) if word[i] != c for c in letters}

With variable word as the original variable to be replaced (e.g. ‘can’) and string letters = 'abcdefghijklmnopqrstuvwxyz'

The above code, when run, gives an error: “local variable ‘c’ referenced before assignment”.

I also found a way to complete the exercise by removing the word[i] != c comparison and then adding 1 line of code to remove word from replace_set. But I still want to complete the question with only 1 line of code. Can someone please help me explain why the above code is failing?

The learner has been helped in a DM.

Hi , Do_Thai_Giang

The error message “local variable ‘c’ referenced before assignment” means that the variable c is being used before it has been assigned a value. This is happening because the for loop in your code is iterating over the letters in the string letters, and each time it iterates, it is assigning a new value to the variable c. However, the for loop is also trying to use the variable c in the word[:i] + c + word[i+1:] expression before it has been assigned a value. This is why you are getting the error message.

To fix this error, you need to make sure that the variable c has a value before it is used in the word[:i] + c + word[i+1:] expression. One way to do this is to move the for loop inside the if statement. This will ensure that the variable c has a value before it is used in the expression.

Thanks for your advise! I understood where the error is.