Python C API has PyDict_Merge (https://docs.python.org/3/c-api/dict.html#c.PyDict_Merge) function which has different behavior than the proposed Python level method (doesn't copy but merge in-place). This is a red flag for me.
On Tue, Mar 5, 2019 at 12:24 PM fhsxfhsx <fhsxf...@126.com> wrote: > > I agree so much on your opinion that I was just to create a topic about this > if you didn't. > I also propose here a small modification to make it more general which adds > an argument `how` (name to be discussed), telling how to merge the dicts, as > many have pointed out that there could be different ways to merge dicts. > So things would be like > > def addition_merge(key, values, exists): > """ > :param key: the key to merge > :param values: values of dicts to merge indexed at `key` > :param exists: whether each dict contains `key` > """ > if any(exists): > return True, sum([value for exist, value in zip(exists, values) > if exist]) > else: > return False > d1.merge(d2, d3, ..., how=addition_merge) > > We could even have > > def discard(key, values, exists): > return not any(exists[1:]), values[0] > d1.merge(d2, how=discard) > > which does the same thing as proposed `d1-d2`. > > This would make things like > d = d1.merge(iter_of_pairs) > d = d1.merge(key=value) > not working, but people could easily wrap a `dict()` over the iterator or > key-value stuff and attach no complication. > > > At 2019-03-05 15:39:40, "INADA Naoki" <songofaca...@gmail.com> wrote: > >I think some people in favor of PEP 584 just want > >single expression for merging dicts without in-place update. > > > >But I feel it's abuse of operator overload. I think functions > >and methods are better than operator unless the operator > >has good math metaphor, or very frequently used as concatenate > >strings. > > > >This is why function and methods are better: > > > >* Easy to search. > >* Name can describe it's behavior better than abused operator. > >* Simpler lookup behavior. (e.g. subclass and __iadd__) > > > >Then, I propose `dict.merge` method. It is outer-place version > >of `dict.update`, but accepts multiple dicts. (dict.update() > >can be updated to accept multiple dicts, but it's not out of scope). > > > >* d = d1.merge(d2) # d = d1.copy(); d.update(d2) > >* d = d1.merge(d2, d3) # d = d1.copy(); d.update(d2); d2.update(d3) > >* d = d1.merge(iter_of_pairs) > >* d = d1.merge(key=value) > > > > > >## Merits of dict.merge() over operator + > > > >* Easy to Google (e.g. "python dict merge"). > >* Easy to help(dict.merge). (or dict.merge? in IPython) > >* No inefficiency of d1+d2+d3+...+dN, or sum(list_of_many_dicts) > >* Type of returned value is always same to d1.copy(). No issubclass, > >no __iadd__. > > > >## Why not dict.updated()? > > > >sorted() is a function so it looks different from L.sort() > >But d.updated() is very similar to d.update() for human eyes. > > > >## How about d1 - d2? > > > >If it is really useful, it can be implemented as method too. > > > >dict.discard(sequence_of_keys) > > > >Regards, > >-- > >INADA Naoki <songofaca...@gmail.com> > >_______________________________________________ > >Python-ideas mailing list > >Python-ideas@python.org > >https://mail.python.org/mailman/listinfo/python-ideas > >Code of Conduct: http://python.org/psf/codeofconduct/ > > > > > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ -- Thanks, Andrew Svetlov _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
