Read and overwrite a file in Python

问题

Currently I'm using this:

f = open(filename, 'r+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.close()

But the problem is that the old file is larger than the new file. So I end up with a new file that has a part of the old file on the end of it.

回答1:

If you don't want to close and reopen the file, to avoid race conditions, you could truncate it:

f = open(filename, 'r+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.truncate()
f.close()

The functionality may also be cleaner and safer using with open as per mVChr's comment, which is will close the handler, even if an error occurs.

with open(filename, 'r+') as f:
    text = f.read()
    text = re.sub('foobar', 'bar', text)
    f.seek(0)
    f.write(text)
    f.truncate()

回答2:

Probably it would be easier and neater to close the file after text = re.sub('foobar', 'bar', text), re-open it for writing (thus clearing old contents), and write your updated text to it.

回答3:

The fileinput module has an inline mode for writing changes to the file you are processing without using temporary files etc. The module nicely encapsulates the common operation of looping over the lines in a list of files, via an object which transparently keeps track of the file name, line number etc if you should want to inspect them inside the loop.

import fileinput
for line in fileinput.FileInput("file",inplace=1):
    if "foobar" in line:
         line=line.replace("foobar","bar")
    print line

回答4:

Try writing it in a new file..

f = open(filename, 'r+')
f2= open(filename2,'a+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.close()
f2.write(text)
fw.close()

来源：https://stackoverflow.com/questions/2424000/read-and-overwrite-a-file-in-python

标签

python

file

overwrite