file.replace（'abcd'）也替换为'abcde'如何仅替换精确值？

Question

def censor2(filename):
    infile = open(filename,'r')
    contents = infile.read()
    contentlist = contents.split()
    print (contents)
    print (contentlist)
    for letter in contentlist:
        if len(letter) == 4:
            print (letter)
            contents = contents.replace(letter,'xxxx')
    outfile = open('censor.txt','w')
    outfile.write(contents)
    infile.close()
    outfile.close()

This code works in Python. It accepts a file 'example.txt', reads it and loops through replacing all 4 letter words with the string 'xxxx' and outputting this into a new file (keeping original format!) called censored.txt.

I used the replace function and find the words to be replaced. However, the word 'abcd' is replaced and the next word 'abcde' is turned into 'xxxxe'

How do i prevent 'abcde' from being changed?

I could not get the below examples to work, but after working with the re.sub module i found that the following code works to replace only 4 letter words and not 5 letter words.

contents = re.sub(r"(\b)\w{4}(\b)", r"\1xxxxx\2", contents)

Answer 1

how about:

re.sub(r'\babcd\b','',my_text)

this will require it to have word boundaries on either side

Answer 2

This is where regular expressions can be helpful. You would want something like this:

import re
...
contents = re.sub(r'\babcd\b', 'xxxx', contents)
....

The \\b is the "word boundary" marker. It matches the change from a word to whitespace characters, punctuation, etc.

You'll need the r'' style string for the regex pattern so that the backslashes are not treated as escape characters.