[Python-ideas] Introduce collections.Reiterable

[Ryan]

At that rate, why not just check for callability(?) in the first place?

Andrew Barnert <abarnert at yahoo.com> wrote:

>On Sep 21, 2013, at 13:02, Ryan <rymg19 at gmail.com> wrote:
>
>> The problem with the try...except statement is that it'll catch
>errors that occur inside the function.
>> Say the function calls zip and accidentally gives an int instead of
>their list. It'll raise a TypeError, which will be caught and a
>CallbackError will be raised.
>
>You can always use EAFP with a bit of "look back after you leaped" to
>help diagnose the error:
>
>try:
>    self.call[item]()
>except TypeError as e:
>    if not callable(self.call[item]):
>        raise CallbackError(...) from e
>    raise
>
>I'm not sure that would be appropriate in this case, but similar code
>is very common when dealing with, e.g., the filesystem (especially in
>2.x, where you had to distinguish errors on errno... but even in 3.x
>it's often worth telling the user that his error was because the folder
>be specified doesn't exist, as opposed to just the filename being
>wrong).
>
>But anyway, I think this is way off topic for this thread. We already
>have both EAFP and LBYL mechanisms for dealing with iteration; the
>argument isn't which one you should use, but whether the existing ABCs
>are sufficient or leave an important gap if you choose to use them for
>LBYL.
>
>> But, in some programs, that behavior doesn't work.
>> 
>> "Stephen J. Turnbull" <stephen at xemacs.org> wrote:
>>> 
>>> Ryan writes:
>>> 
>>>> I can still see why checking if its callable is a good idea in some
>>>> cases.
>>> 
>>> You can always rewrite the LBYL in EAFP form:
>>> 
>>> try:
>>> self.call[item]()
>>> except TypeError as e:
>>> raise CallbackError(...) from e
>>> 
>>> This is definitely preferred if you can enclose a whole suite in a
>try
>>> and expect the CallbackError to be infrequent, eg:
>>> 
>>> try:
>>> while item in input:
>>> self.call[item]()
>>> except TypeError as e:
>>> raise CallbackError(...) from e
>>> 
>>> However, what you probably really want to do (which is a better
>>> argument for LBYL, anyway) is
>>> 
>>> if callable(callback):
>>> self.call[item] = callback
>>> else:
>>> what_would_jruser_do()
>> 
>> -- 
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-- 
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