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file opening and closing

Donn Cave donn at drizzle.com
Thu Dec 25 00:20:55 EST 2003 
Quoth anton muhin <antonmuhin at rambler.ru>:
| hokieghal99 wrote:
|> jpg = string.find(file(os.path.join(root,fname), 'rb').read(), 'JFIF')
|> 
|> Should this file be closed after reading? If so, how would one close it?
|> What's the downside to not closing it?
|
| It would, then the file object gets destroyed (it method __del__ is 
| called). However, as Python uses garbage collection, it can happen much 
| later after you leave the function.
|
| There is mostly no downsides except for the cases when you try to read 
| this file---it might not be flashed.

(Flushed, that is, and of course that wouldn't be a problem here since
the file is only to be read.)  Note that the exact behavior here depends
on the implementation:  Java Python may as you say defer the close
indefinitely, but C Python will execute it immediately on function return,
because its garbage collection is based on reference count.

The above usage is fine in C Python.  In Java Python, it's probably OK
but potential problems would include file descriptor resource starvation
if opening many files this way, and low disk space if reading large files
this way and then deleting them, because the open file descriptor will
preserve the actual file even though its directory entry is gone.

	Donn Cave, donn at drizzle.com
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