Q on explicitly calling file.close

[Gabriel Genellina]

En Sun, 06 Sep 2009 21:20:52 -0300, Stephen Hansen <apt.shansen at gmail.com>
escribió:
> On Sun, Sep 6, 2009 at 4:31 PM, r <rt8396 at gmail.com> wrote:
>> On Sep 6, 1:14 pm, "Jan Kaliszewski" <z... at chopin.edu.pl> wrote:
>> > 05-09-2009 r <rt8... at gmail.com> wrote:

>> > > i find the with statement (while quite useful in general
>> > > practice) is not a "cure all" for situations that need and exception
>> > > caught.
>
> But what does that even mean? What's the -problem- that it isn't  
> 'curing'?
> That 'with' doesn't completely replace all uses of 'try'? It was never  
> meant
> to-- that seems like a completely different problem area. But, if you do
> want it to handle exception catching, that's just a question of making a
> context manager that does so.
>
>     import contextlib
>
>     @contextlib.contextmanager
>     def file_with_errorhandling(filename, mode,
> exceptions=(IOError,OSError)):
>         fp = file(filename, mode)
>         try:
>             yield fp
>         except exceptions:
>             print "Handle file-operation errors gracefully here."
>         fp.close()
>
>     with file_with_errorhandling(filename, 'r') as fp:
>         fp.read() # or whatever
>
> True, the context manager provided by file objects just lets exceptions
> propagate up but that's usually the desired behavior. You can make  
> context
> managers for particular problems you run across that handle exceptions if
> you want.

Note that to correctly emulate the file built-in context manager,
fp.close() should be inside a finally clause.

> The with statement isn't about never having to type try again, I don't
> think.

The with statement is intended as a replacement for common try/finally
blocks, not try/except blocks as the OP seems to imply.

-- 
Gabriel Genellina