python列表索引必须是整数而不是字符串

Question

I'm trying to write a basic algorithm for encrypting a file. It takes the ASCII value of each character in a string and moves it up or down an amount depending on how long the password is, then you can layer more passwords on top.

def encrypt(s):
    lenStr=s.__len__() #used later for working how far the int is moved
    s=list(s) #converts the string to a list
    for x in s:
        s[x]=ord(s[x]) #the same index of the list is = to the value of the string
        s[x]=chr(s[x])#is where it eventualy gets changed back to a str

s=ord(s) is the line which is throwing the error, i added int() around it but didnt help, same error

Answer 1

x is a character from the string, not an integer. Let me illustrate:

>>> s = list('abcd')
>>> for x in s:
...     print(x)
...
a
b
c
d
>>>

You want x to be integer values from 0 to the length of the string, like this:

>>> for x in range(len(s)):
...     print(x)
...
0
1
2
3
>>>

So, your function should probably look like this (untested):

def encrypt(s):
    lenStr=s.__len__() #used later for working how far the int is moved
    s=list(s) #converts the string to a list
    for x in range(len(s)):
        s[x]=ord(s[x]) #the same index of the list is = to the value of the string
        s[x]=chr(s[x])#is where it eventualy gets changed back to a str

Answer 2

I am guessing this is what you are aiming for:

def encrypt(s):
    offset = len(s)
    return ''.join(chr(ord(c) + offset) for c in s)

def decrypt(s):
    offset = len(s)
    return ''.join(chr(ord(c) - offset) for c in s)

Some tips:

• Use len(s) instead of lenStr=s.__len__()
• Naming values near their first use in the code improves readability.
• Choose names that describe the use of the value.
• Strings are iterable, same as lists. No need to convert a string into a list.
• Learn and use list comprehensions and generators whenever possible, they are usually much faster, simpler, easier to read and less error prone to create.
• Remember to accept and/or upvote answers that are helpful.

Answer 3

You're getting the TypeError exception because the value of x in the s[x]=ord(s[x]) statement is one of the elements of the s list, so it's an individual character from the string argument passed to encrypt() . To fix that, just loop through all the possible indices of the s list which happens to be the same as the length as the original string:

def encrypt(s):
    lenStr=len(s)
    s=list(s) # convert the string to a list
    for i in range(lenStr):
        s[i]=ord(s[i])
        s[i]=chr(s[i])

This will allow your code to run without getting that error. From your description of the encryption algorithm you're going to implement, one thing to watch out for is producing illegal 8-bit character values out of the range of 0-255. You can avoid that problem by simply applying the mod operator % to the intermediate results to keep the values in the proper range. Here's what I mean:

def encrypt(s):
    lenStr = len(s)
    s = list(s) # convert the string to a list
    for i in range(lenStr):
        s[i] = chr((ord(s[i]) + lenStr) % 256)
    return ''.join(s) # convert list back into a string

Likewise, you'll have to do the same thing when you decrypt a string:

def decrypt(s):
    lenStr = len(s)
    s = list(s) # convert the string to a list
    for i in range(lenStr):
        s[i] = chr((ord(s[i]) - lenStr) % 256)
    return ''.join(s) # convert list back into a string

enc = encrypt('Gnomorian')
print('encrypted:', enc)
dec = decrypt(enc)
print('decrypted:', dec)

Output:

encrypted: Pwxvx{rjw
decrypted: Gnomorian

Also note that not all the characters whose ord() values are in the range of 0-255 are printable, so you may want to restrict the encryption transformation even more if that's a requirement (that the encrypted version be printable).