exar...@twistedmatrix.com wrote: > On 08:45 am, tjre...@udel.edu wrote: >> Tom Machinski wrote: >>> In most cases, `list(generator)` works as expected. Thus, >>> `list(<generator expression>)` is generally equivalent to `[<generator >>> expression>]`. >>> >>> Here's a minimal case where this equivalence breaks, causing a serious >>> and hard-to-detect bug in a program: >>> >>> >>> def sit(): raise StopIteration() >> >> StopIteration is intended to be used only within the .__next__ method >> of iterators. The devs know that other 'off-label' use results in the >> inconsistency you noted, but their and my view is 'don't do that'. > > Which is unfortunate, because it's not that hard to get StopIteration > without explicitly raising it yourself and this behavior makes it > difficult to debug such situations. > > What's with this view, exactly? Is it just that it's hard to implement > the more desirable behavior?
I'm not exactly sure what you're asking for. The StopIteration exception originated as part of the for-loop protocol. Later on it was generalized to apply to generators as well. The reason for using an exception is simple: raising and catching exceptions is fast at C level and since the machinery for communicating exceptions up the call stack was already there (and doesn't interfere with the regular return values), this was a convenient method to let the upper call levels know that an iteration has ended (e.g. a for-loop 4 levels up the stack). I'm not sure whether that answers your question, but it's the reason for things being as they are :-) -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Dec 14 2009) >>> Python/Zope Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::: Try our new mxODBC.Connect Python Database Interface for free ! :::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
