On Oct 14, 5:01 am, Steven D'Aprano <[EMAIL PROTECTED]
cybersource.com.au> wrote:
> I have found myself writing functions rather like these:
>
> def openfile(filename):
> if filename == '-':
> # convention for shell scripts in Unix-land is to use
> # '-' for stdin/stdout for reading/writing.
> outfile = sys.stdout
> if filename == '2-':
> outfile = sys.stderr
> else:
> outfile = file(filename, 'w')
> return outfile
>
> def closefile(fileobj):
> # don't close standard file objects, or their replacements
> if not fileobj in (sys.stdout, sys.stderr, sys.stdin,
> sys.__stdout__, sys.__stderr__, sys.__stdin__):
> fileobj.close()
>
> def processfile(filename):
> outfile = openfile(filename)
> try:
> # lots of processing here, which may raise exceptions
> var = "stuff happens"
> outfile.write(var)
> finally:
> closefile(outfile)
>
> A question:
>
> I know I'm being paranoid about not closing files I shouldn't close, but
> am I being excessively paranoid, or not paranoid enough?
>
> Suggestions for improvements welcome; while I'm happy to read suggestions
> using the new with statement, I can't yet rely on having Python 2.5 or
> better so I have to stick to try...finally.
With with:
import sys
class leave_open(object):
def __init__(self, obj):
self.obj = obj
def __enter__(self):
return self.obj
def __exit__(self, *exc_info):
pass
def open_file(name, special={'-':sys.stdout, '2-':sys.stderr}):
if name in special:
return leave_open(special[name])
else:
return open(name, 'w')
def process_file(filename):
with open_file(filename) as outfile:
outfile.write("stuff happens")
Without with:
import sys
def open_file(name, special={'-':sys.stdout, '2-':sys.stderr}):
if name in special:
return False, special[name]
return True, open(name, 'w')
def process_file(filename):
should_close, outfile = open_file(filename)
try:
outfile.write('stuff happens')
finally:
if should_close:
outfile.close()
--
Paul Hankin
--
http://mail.python.org/mailman/listinfo/python-list
