try: finally: question

djw donald.welch at
Wed Jul 7 20:20:41 CEST 2004

Peter Hansen wrote:

> djw wrote:
>> Peter Hansen wrote:
>>>Hmm... Also, I think it really *is* unusual (as in, "not usual"
>>>meaning not really common) to nest try blocks.
>> I am suprised that what I am trying to accomplish is unusual. Basically,
>> I want to acquire some resource/object (that requires cleanup).
> It *is* unusual, in the way I mean, because relatively little code
> is involved with resource cleanup when it's required (in Python,
> anyway), and relatively little resource cleanup is required when
> programming, in general.

I would agree (with regards to straight Python), but I disagree when you
include I/O. The I/O I am interacting with requires cleanup. Simply
allowing the device object I created to go out of scope and be
automatically cleaned up does not cause the I/O to be cleaned up properly.

>> This seems like a really normal bit of code to me.
> Maybe I'm drawing too fine a line here.  I'm using "usual" and
> "unusual" in the sense of "frequently occurring or not", rather than
> in the sense of "normal or really weird".
> It's very normal.  It's just not so frequently occurring that
> the nested finally/except should be seen as a major roadblock.
> Not that one example tells much about the general case, but: I
> just wrote a little inventory-tracking application, very small.
> It has one finally (for a database commit), and two excepts
> (basically around things that could have been if/thens but
> are slightly cleaner as exception handling code).  None of
> these cases required bringing in a nested try.  I think that's
> the "usual" pattern.
> If you find yourself needing to write such things very often,
> I think you're probably not writing your code in a very modular
> way, as it would then be more reusable and therefore require
> being written much less often...

Point taken. Its not that I'm doing this that often, its just when I do it
seems awkward. Since I find most Python code to be rather elegant and
concise, awkward situations like this tend to stick out glaringly to me.


> -Peter

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