On Fri, Jul 13, 2018 at 12:38 PM, Michael Selik <m...@selik.org> wrote:
> Thanks for linking to these. > yup -- real use cases are really helpful. Though the other paradigm for grouping is use of setdefault() rather than defaultdict. So it would be nice to look for those, too. > I looked at many of them in my own research, but for some reason didn't > think to write down the links. I'll respond to each one separately. > > Throughout, I'm going to use my proposed ``grouped`` builtin to > demonstrate possible revisions. Note that I am *not* suggesting a > replacement to defaultdict. The proposal is to make a common task easier > and more reliable. It does not satisfy all uses of defaultdict. > agreed -- and it shouldn't. I"d like to see how some of these pan our with my proposed API: either a Grouped class, or at least (key, value) iterables and/or a value function. I don't have time now to do them all, but for the moment: I noticed recently that *all* examples for collection.defaultdict ( >> https://docs.python.org/3.7/library/collections.html# >> collections.defaultdict) are cases of grouping (for an int, a list and a >> set) from an iterator with a key, value output. >> > and yet others on this thread think a (key, value) input would be rare -- I guess it depends on whether you are thinking dict-like already.... > >> https://frama.link/o3Hb3-4U, >> > > accum = defaultdict(list) > garbageitems = [] > > for item in root: > filename = findfile(opts.fileroot, item.attrib['classname']) > accum[filename].append(float(item.attrib['time'])) > if filename is None: > garbageitems.append(item) > > > This might be more clear if separated into two parts. > > def keyfunc(item): > return findfile(opts.fileroot, item.attrib['classname']) > groups = grouped(root, keyfunc) > groups = {k: [float(v.attrib['time']) for v in g] for k, g in > groups.items()} > garbage = groups.pop(None, []) > so this one is a prime case for a value function -- I think post-processing the groups is a pretty common case -- why make people post-process it? def keyfunc(item): return findfile(opts.fileroot, item.attrib['classname']) def valuefunc(item): float(item.attrib['time']) groups = grouped(root, keyfunc, valuefunc) garbage = groups.pop(None, []) And the post-processing is then mixing comprehension style with key function style (what to call that -- "functional" style?), so why not use a (key, value) iterable: groups = grouped((findfile(opts.fileroot, item.attrib['classname']), item.attrib['time']) for item in root)) OK -- that's packing a bit too much into a line, so how about: def keyfunc(item): return findfile(opts.fileroot, item.attrib['classname']) groups = grouped( (keyfunc(item), item.attrib['time']) for item in root) > > self.mapping = collections.defaultdict(set) > for op in (op for op in graph.get_operations()): > if op.name.startswith(common.SKIPPED_PREFIXES): > continue > for op_input in op.inputs: > self.mapping[op_input].add(op) > > > This is a case of a single element being added to multiple groups, which > is your section B, below. The loop and filter could be better. It looks > like someone intended to convert if/continue to a comprehension, but > stopped partway through the revision. > yeah, this is weird -- But it does make a case for having a class with the option f using a set to collect (which I have in an older commit of my prototype: inputs = ((op_input, op) for op in ops for op_input in op.inputs) groups = Grouping(inputs, key=itemgetter(0), collection=set) otherwise, you could have a method to do it: groups.map_on_groups(set) (not sure I like that method name, but I hope you get the idea) OK, back to work. -CHB -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
_______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
