Op 2005-01-18, Nick Coghlan schreef <[EMAIL PROTECTED]>: > Raymond Hettinger wrote: >> [Delaney, Timothy C] >> >>>Nick's other suggestion - that genexps propagate __len__ - might >>>still be interesting. Of course, it would only be applicable for >>>unconditional genexps(i.e. no if clause). >> >> Length transparency for iterators is not as general as one would expect. I >> once >> spent a good deal of effort exploring where it made sense, and I was >> surprised >> to find that it only rarely works out. Length transparency is an >> unexpectedly >> thorny subject with many dead-ends which precludes a fully general solution >> such >> as that proposed by Nick. >> >> For a recap of my research, see the docstring for Lib/test/test_iterlen.py . > > """The situation slightly more involved whenever an object allows length > mutation during iteration. """ > > Ouch. Nice understatement. > > It's rather unfortunate that we can't make use of the length information even > when the source *doesn't* mutate, though. I'll have to think some more to see > if > I can come up with any concrete ideas for you to shoot down :)
Something else I was thinking about. I think it would be nice if the python compilor could figure out whether a genexp in a list or tuple expression always generates the same list or tuple and then instead of generating code would generate the list or tuple in place. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
