My first Python program

Jonas H. jonas at lophus.org
Wed Oct 13 19:49:13 CEST 2010


On 10/13/2010 06:48 PM, Seebs wrote:
> Is it safe for me to assume that all my files will have been flushed and
> closed?  I'd normally assume this, but I seem to recall that not every
> language makes those guarantees.

Not really. Files will be closed when the garbage collector collects the 
file object, but you can't be sure the GC will run within the next N 
seconds/instructions or something like that. So you should *always* make 
sure to close files after using them. That's what context managers were 
introduced for.

     with open('foobar') as fileobject:
         do_something_with(fileobject)

basically is equivalent to (simplified!)

     fileobject = open('foobar')
     try:
         do_something_with(fileobject)
     finally:
         fileobject.close()

So you can sure `fileobject.close()` is called in *any* case.

>> * you might want to pre-compile regular expressions (`re.compile`)
>
> Thought about it, but decided that it was probably more complexity than I
> need -- this is not a performance-critical thing.  And even if it were, well,
> I'm pretty sure it's I/O bound.  (And on my netbook, the time to run this
> is under .2 seconds in Python, compared to 15 seconds in shell, so...)

Forget about my suggestion. As someone pointed out in a another post, 
regular expressions are cached anyway.

> I'm a bit unsure as to how to pick the right subclass, though.

There are a few pointers in the Python documentation on exceptions.

Jonas



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