我的变种，在整个文件中一次一个词。

我把它读进了记忆。

def replace_word(infile,old_word,new_word):
    if not os.path.isfile(infile):
        print ("Error on replace_word, not a regular file: "+infile)
        sys.exit(1)

    f1=open(infile,'r').read()
    f2=open(infile,'w')
    m=f1.replace(old_word,new_word)
    f2.write(m)

正如Jack Aidley发布的和J.F. Sebastian指出的那样，这个代码是行不通的:

 # Read in the file
filedata = None
with file = open('file.txt', 'r') :
  filedata = file.read()

# Replace the target string
filedata.replace('ram', 'abcd')

# Write the file out again
with file = open('file.txt', 'w') :
  file.write(filedata)`

但这段代码将工作(我已经测试过了):

f = open(filein,'r')
filedata = f.read()
f.close()

newdata = filedata.replace("old data","new data")

f = open(fileout,'w')
f.write(newdata)
f.close()

使用此方法，fileein和fileout可以是同一个文件，因为Python 3.3将在打开进行写入时覆盖该文件。

Besides the answers already mentioned, here is an explanation of why you have some random characters at the end: You are opening the file in r+ mode, not w mode. The key difference is that w mode clears the contents of the file as soon as you open it, whereas r+ doesn't. This means that if your file content is "123456789" and you write "www" to it, you get "www456789". It overwrites the characters with the new input, but leaves any remaining input untouched. You can clear a section of the file contents by using truncate(<startPosition>), but you are probably best off saving the updated file content to a string first, then doing truncate(0) and writing it all at once. Or you can use my library :D

使用re.subn可以对替换过程进行更多的控制，例如将单词分成两行，区分大小写的匹配。此外，它返回匹配的数量，如果没有找到字符串，可以使用这些匹配来避免浪费资源。

import re

file = # path to file

# they can be also raw string and regex
textToSearch = r'Ha.*O' # here an example with a regex
textToReplace = 'hallo'

# read and replace
with open(file, 'r') as fd:
    # sample case-insensitive find-and-replace
    text, counter = re.subn(textToSearch, textToReplace, fd.read(), re.I)

# check if there is at least a  match
if counter > 0:
    # edit the file
    with open(file, 'w') as fd:
        fd.write(text)

# summary result
print(f'{counter} occurence of "{textToSearch}" were replaced with "{textToReplace}".')

一些正则表达式:

添加re.I标志，re.IGNORECASE的缩写形式，用于不区分大小写的匹配 对于多行替换re.subn(r'\n*'.join(textToSearch)， textToReplace, fd.read()))，取决于数据也'\n{，1}'。注意，在这种情况下，textToSearch必须是纯字符串，而不是正则表达式!

正如michaelb958所指出的，不能用不同长度的数据替换现有的部分，因为这会使其余部分不合适。我不同意其他人建议你从一个文件读到另一个文件。相反，我将把文件读入内存，修复数据，然后在单独的步骤中将其写入相同的文件。

# Read in the file
with open('file.txt', 'r') as file :
  filedata = file.read()

# Replace the target string
filedata = filedata.replace('abcd', 'ram')

# Write the file out again
with open('file.txt', 'w') as file:
  file.write(filedata)

除非你有一个巨大的文件要处理，它太大了，无法一次性加载到内存中，或者你担心如果在向文件写入数据的第二步过程中中断，可能会导致数据丢失。

Fileinput已经支持就地编辑。在这种情况下，它将stdout重定向到文件:

#!/usr/bin/env python3
import fileinput

with fileinput.FileInput(filename, inplace=True, backup='.bak') as file:
    for line in file:
        print(line.replace(text_to_search, replacement_text), end='')