Python不在文件中写入

Question

Have problem with replacing lines in file. Not sure if changes weren't written in file or data lines weren't replaced. Here is how I tried to do this:

filename = "filename.txt"
f = open(filename, "r+")

lines = [line1, line2, line3]

for line in lines:
    data = f.read()
    new_line = "some new line"
    data.replace(line, new_line)

f.write(data)
f.close()

Where could the problem be?

Answer 1

The replace function doesn't make changes in the object itself, but it returns a new string. So what you need is:

data = data.replace(line, new_line)

And taking Roger's comment, your code should look like this:

filename = "filename.txt"
f = open(filename, "r+")

lines = [line1, line2, line3]
data = f.read()

for line in lines:
    new_line = "some new line"
    data = data.replace(line, new_line)

f.write(data)
f.close()

Hope it helps.

Answer 2

import fileinput 

for line in fileinput.input( filename , inplace = 1 ):
   print line.replace("SOMETHING", "SOMETHING ELSE" ), # catch for double line breaks

useful for editing files inline.