How to safely open/close files in python 2.4

问题:

I'm currently writing a small script for use on one of our servers using Python. The server only has Python 2.4.4 installed.

I didn't start using Python until 2.5 was out, so I'm used to the form:

with open('file.txt', 'r') as f:
    # do stuff with f

However, there is no with statement before 2.5, and I'm having trouble finding examples about the proper way to clean up a file object manually.

What's the best practice for disposing of file objects safely when using old versions of python?

回答1:

See docs.python.org:

When you’re done with a file, call f.close() to close it and free up any system resources taken up by the open file. After calling f.close(), attempts to use the file object will automatically fail.

Hence use close() elegantly with try/finally:

f = open('file.txt', 'r')

try:
    # do stuff with f
finally:
    f.close()

This ensures that even if # do stuff with f raises an exception, f will still be closed properly.

Note that open should appear outside of the try. If open itself raises an exception, the file wasn't opened and does not need to be closed. Also, if open raises an exception its result is not assigned to f and it is an error to call f.close().

回答2:

In the above solution, repeated here:

f = open('file.txt', 'r')

try:
    # do stuff with f
finally:
   f.close()

if something bad happens (you never know ...) after opening the file successfully and before the try, the file will not be closed, so a safer solution is:

f = None
try:
    f = open('file.txt', 'r')

    # do stuff with f

finally:
    if f is not None:
       f.close()

回答3:

Here is example given which so how to use open and "python close

from sys import argv
script,filename=argv
txt=open(filename)
print "filename %r" %(filename)
print txt.read()
txt.close()
print "Change the file name"
file_again=raw_input('>')
print "New file name %r" %(file_again)
txt_again=open(file_again)
print txt_again.read()
txt_again.close()

It's necessary to how many times you opened file have to close that times.