Me too when I'm lazy but we shouldn't; it happens to work fine on CPython but on implementations use garbage collection instead of reference counting (e.g. Jython) it leaks file handlers. The "with" statement is the right cross-platform way to handle resources.
Perhaps in this case - but how about a case where you partially iterate over the file, but then the file object goes out of scope? CPython would close (and free) that immediately, but other implementations probably wouldn't.
While editing the answer to masklinn comment, this case came to me. You both are, of course, right. There is no reliable way to close the file from the for iterator.
Indeed. In generational garbage collectors, the file object may remain until the collector decides to collect it. But isn't the file object also raising a StopIteration error? Shouldn't it at least close itself then?
You can always fp.seek(0) and iterate again. Iteration and file openness are separate concepts, and any API worth its salt (e.g. the python file api) keeps it that way.
If you've opened that file in the right mode, you can conceivably append to it once you reach its end. Even in read only mode, I imagine you may conceivably seek back for further reading?
As far as iteration goes, there is no difference between
for line in open(somepath):
# stuff
and
f = open(somepath)
for line in f:
# stuff
and the second case would be outright broken if the file just decided to close itself when it stops iterating (as others noted, the developer may now want to append new content, or use file.seek and fly around the file's content).
Not to mention a major issue: `break`. The iterator gets no mention of breaks and the iteration is not terminated at this point (as far as the iterator is concerned, that is) so adding a `break` to your iteration (to stop it early because you've found the data/line you needed in a linear search) would suddenly start leaking file handlers where those were collected beforehand... not good.
For that to work as it does in CPython, the file would have to know it has no name reference attached to it and that its scope is limited to the iteration and that it can close the file when the iteration ends. I'd love to have this idiom supported under other implementations - it's beautiful.
> For that to work as it does in CPython, the file would have to know it has no name reference attached to it and that its scope is limited to the iteration and that it can close the file when the iteration ends.
Which will never happen and really has nothing to do with iteration (or the file object itself)
> I'd love to have this idiom supported under other implementations - it's beautiful.
I disagree on its beauty, but beyond that I can assure you it's never going to be a property of python-the-language.
