如何正确替换字符串中的字符？

Question

I am new to programming in general, and couldn't figure out how to replace multiple characters in a string. Using the string.replace("x", "y") function, I tried to make a simple encoder:

phrase = "abcdef"
phrase.replace("a", "b")
phrase.replace("b", "c")
phrase.replace("c", "d")
phrase.replace("d", "e")
phrase.replace("e", "f")
phrase.replace("f", "g")

print(phrase)

I was expecting the output to be:

"bcdefg"

but instead got

"abcdef"

This was best I could come up with and it does not work. I looked around other questions and the answers were too confusing. Please help and explain what i am doing wrong.

Answer 1

For python 3 you can use str.maketrans and str.translate (links below) - for python 2 you can find them inside the string module:

# from string import maketrans, translate # python 2, in python 3 they are on str

trans = str.maketrans("abcdef","bcdefg")

phrase = "abcdef"

print(str.translate(phrase, trans)) # outputs: bcdefg

See

• str.maketrans
• str.translate

Answer 2

You have to replace the string with the output of phrase.replace() . Since phrase is a string, it does not get updated as strings are immutable. You also have to change the order of your replacements or you get gggggg as a result:

phrase = "abcdef"
phrase = phrase.replace("f", "g")
phrase = phrase.replace("e", "f")
phrase = phrase.replace("d", "e")
phrase = phrase.replace("c", "d")
phrase = phrase.replace("b", "c")
phrase = phrase.replace("a", "b")

print(phrase)

bcdefg

Answer 3

replace函数返回一个新字符串，该字符串是前一个字符替换后的字符串的副本，因此您的代码应为@depperm所述：

phrase = phrase.replace("f", "g").replace("e", "f").replace("d", "e").replace("c", "d").replace("b", "c").replace("a", "b")

Answer 4

Just made a quick search for you and found this Change each character in string to the next character in alphabet

where @dawg put this:

from string import ascii_lowercase as letters

s='abcxyz'
ns=''
for c in s:
    if c in letters:
        ns=ns+letters[(letters.index(c)+1)%len(letters)]
    else:
        ns+=c

Tested it and worked fine, ns value is 'bcdyza'

Answer 5

If you're trying to learn python a great tool to use in the python repl. In this case there's nothing wrong with the replace method, it's your logic that's incorrect. So let's see what's going on in the repl.

>>> phrase = "abcdef"
>>> phrase.replace("a", "b")
'bbcdef'
>>> phrase.replace("b", "c")
'accdef'
>>> phrase.replace("c", "d")
'abddef'
>>> phrase.replace("d", "e")
'abceef'
>>> phrase.replace("e", "f")
'abcdff'
>>> phrase.replace("f", "g")

The correct algorithm for this kind of caesar cipher would be something like.

s = ''
for i in range(len(phrase)):
   s += chr(ord(phrase[i])+1)

Hope this helps.