在列表的每个元素上使用 function

Question

I have a list ( decrypted_list ) which contains four integer elements I have to decrypt. The function's job is to decrypt the code, and it's logic is correct. After defining the function, I want to call it on every element of decrypted_list to decrypt its elements.

encrypted_list = [7, 1, 0, 2]

def decrypter(number):
    for number in encrypted_list:
        if (number + 4) < 10:
            return (number + 4)
        elif (number + 4) > 10:
            return (number + 4) % 10

decrypted_list = [decrypter(x) for x in encrypted_list]

However, the output is not what I expect:

Expected: [1, 5, 4, 6]
Actual: [1, 1, 1, 1]

Please help. I am new to Python: :)

Answer 1

There is no point in looping over encrypted_list in your decrypter function. This function should just look at the number argument - it does not need to know about the encrypted_list variable.

The loop operation itself should only take place in your list comprehension ( [decrypter(x) for x in encrypted_list] ).

Change your function to the following and you should be fine:

def decrypter(number):
  if (number + 4) < 10:
      return (number + 4)
  elif (number + 4) > 10:
      return (number + 4) % 10

Answer 2

Your function should look like this:

def decrypter(number):
    if (number + 4) < 10:
        return (number + 4)
    elif (number + 4) > 10:
        return (number + 4) % 10

You shouldn't use a for loop here because you are going to use this function on each element of the list in the last line of your code:

decrypted_list = [decrypter(x) for x in encrypted_list]

As you have said, that function only decrypts one number, so it doesn't need to know about the whole list. encrypted_list should not appear in that function.

Adding that for loop in will cause the function's behaviour to change - whatever number you pass in, it will only decrypt the number 1 , because that is the first item of the list. The for loop doesn't actually loop through the list, because it hits return on the first iteration.

Answer 3

Others already pointed out the problem in your code. I'd like to point out a redundancy in your function. This would produce the same output: decrypted_list = [(x + 4) % 10 for x in encrypted_list] . Or if you want to have in a function:

def decrypter(number):
    return (number + 4) % 10

decrypted_list = [decrypter(x) for x in encrypted_list]

Since x % 10 == x if x < 10 .