Question

Some code:

import cStringIO

def f():
    buffer = cStringIO.StringIO()
    buffer.write('something')
    return buffer.getvalue()

The documentation says:

StringIO.close(): Free the memory buffer. Attempting to do further
operations with a closed StringIO object will raise a ValueError.

Do I have to do buffer.close(), or it will happen automatically when buffer goes out of scope and is garbage collected?

UPDATE:

I did a test:

import StringIO, weakref

def handler(ref):
    print 'Buffer died!'

def f():
    buffer = StringIO.StringIO()
    ref = weakref.ref(buffer, handler)
    buffer.write('something')
    return buffer.getvalue()

print 'before f()'
f()
print 'after f()'

Result:

vic@wic:~/projects$ python test.py 
before f()
Buffer died!
after f()
vic@wic:~/projects$

Answer 1

Generally it’s still better to call close() or use the with statement, because there may be some unexpected behaviour in special circumstances. For example, the expat-IncrementalParser seems to expect a file to be closed, or it won’t return the last tidbit of parsed xml until a timeout occurs in some rare circumstances.

But for the with-statement, which handles the closing for you, you have to use the StringIO class from the io-Modules, as stated in the comment of Ivc.

This was a major headache in some legacy sax-parser script we solved by closing the StringIO manually.

The “out-of-scope” close didn’t work. It just waited for the timeout-limit.