Change one character in a string?

问题:

What is the easiest way in Python to replace a character in a string like:

text = "abcdefg"; text[1] = "Z";            ^

回答1:

Don't modify strings.

Work with them as lists; turn them into strings only when needed.

>>> s = list("Hello zorld") >>> s ['H', 'e', 'l', 'l', 'o', ' ', 'z', 'o', 'r', 'l', 'd'] >>> s[6] = 'W' >>> s ['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd'] >>> "".join(s) 'Hello World'

Python strings are immutable (i.e. they can't be modified). There are a lot of reasons for this. Use lists until you have no choice, only then turn them into strings.

回答2:

new = text[:1] + 'Z' + text[2:]

回答3:

Fastest method?

There are three ways. For the speed seekers I recommend 'Method 2'

Method 1

Given by this answer

text = 'abcdefg' new = list(text) new[6] = 'W' ''.join(new)

Which is pretty slow compared to 'Method 2'

timeit.timeit("text = 'abcdefg'; s = list(text); s[6] = 'W'; ''.join(s)", number=1000000) 1.0411581993103027

Method 2 (FAST METHOD)

Given by this answer

text = 'abcdefg' text = text[:1] + 'Z' + text[2:]

Which is much faster:

timeit.timeit("text = 'abcdefg'; text = text[:1] + 'Z' + text[2:]", number=1000000) 0.34651994705200195

Method 3:

Byte array:

timeit.timeit("text = 'abcdefg'; s = bytearray(text); s[1] = 'Z'; str(s)", number=1000000) 1.0387420654296875

回答4:

Python strings are immutable, you change them by making a copy.
The easiest way to do what you want is probably.

text = "Z" + text[1:]

The text[1:] return the string in text from position 1 to the end, positions count from 0 so '1' is the second character.

edit: You can use the same string slicing technique for any part of the string

text = text[:1] + "Z" + text[2:]

Or if the letter only appears once you can use the search and replace technique suggested below

回答5:

Starting with python 2.6 and python 3 you can use bytearrays which are mutable (can be changed element-wise unlike strings):

s = "abcdefg" b_s = bytearray(s) b_s[1] = "Z" s = str(b_s) print s aZcdefg

edit: Changed str to s

edit2: As Two-Bit Alchemist mentioned in the comments, this code does not work with unicode.

回答6:

Like other people have said, generally Python strings are supposed to be immutable.

However, if you are using CPython, the implementation at python.org, it is possible to use ctypes to modify the string structure in memory.

Here is an example where I use the technique to clear a string.

Mark data as sensitive in python

I mention this for the sake of completeness, and this should be your last resort as it is hackish.

回答7:

This code is not mine. I couldn't recall the site form where, I took it. Interestingly, you can use this to replace one character or more with one or more charectors. Though this reply is very late, novices like me (anytime) might find it useful.

Change Text function.

mytext = 'Hello Zorld' mytext = mytext.replace('Z', 'W') print mytext,

回答8:

Actually, with strings, you can do something like this:

oldStr = 'Hello World!'     newStr = ''  for i in oldStr:       if 'a' < i < 'z'