[EMAIL PROTECTED] wrote: > On May 27, 7:50 pm, Raymond Hettinger <[EMAIL PROTECTED]> wrote: > > The groupby itertool came-out in Py2.4 and has had remarkable > > success (people seem to get what it does and like using it, and > > there have been no bug reports or reports of usability problems). > > With due respect, I disagree. Bug ID #1212077 is either a bug report > or a report of a usability problem, depending on your point of view. > You may disagree on whether or not this is a problem that needs to be > be fixed, but it *is* a report. > > http://sourceforge.net/tracker/index.php?func=detail&aid=1212077&group_id=5470&atid=105470 > > > I think the semantics of the itertools groupby are too tricky for > naive users
Itertools isn't targeted primarily at naive users. It can be useful to them, but it's really there to allow sophisticated work on iterables without reading them all in at once (indeed, it works properly on infinite iterables). That's pretty much _the_ defining characteristic of itertools Anyone who's doing that knows you can't do infinite lookahead, so you can't do a sort or a group-by over the entire data set. IOW, for anyone who would be looking to use itertools for what it's designed for, the kind of operation you specify below would be very unexpected. >--I find them confusing myself, and I've been using Python > for quite a while. I still hope that Python will someday gain a > groupby function suitable for ordinary use. Until that happens, I > recommend the following cookbook entry: > > # from http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/259173 > > class groupby(dict): > def __init__(self, seq, key=lambda x:x): > for value in seq: > k = key(value) > self.setdefault(k, []).append(value) > __iter__ = dict.iteritems The itertools groupby is incredibly useful for writing SQL object mappers. It's exactly what I wanted when I first started looking in itertools to see if there was a way to consolidate rows. Also, that recipe goes against the spirit of itertools--if I'm going out of my way to use itertools, it usually means I may be working with very large data sets that I can't read into memory. It's a useful recipe, but it's also likely to be unusable in the context of itertools-related problem domains. -- http://mail.python.org/mailman/listinfo/python-list
