Actually, this was made even more condition-y in 3.8. Now we check __iter__ too:
D.update([E, ]**F) -> None. Update D from dict/iterable E and F. If E is present, has a .keys() method, is a subclass of dict, and hasn't overridden __iter__, then does: for k in E: D[k] = E[k] If E is present, has a .keys() method, and is not a subclass of dict or has overridden __iter__, then does: for k in E.keys(): D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k] Bleh. On Tue, Mar 5, 2019 at 2:54 PM Brandt Bucher <brandtbuc...@gmail.com> wrote: > Should our __sub__ behavior be the same... > > > Sorry, our "__isub__" behavior. Long day... > > On Tue, Mar 5, 2019 at 2:47 PM Brandt Bucher <brandtbuc...@gmail.com> > wrote: > >> These semantics are intended to match those of update as closely as >>> possible. For the dict built-in itself, calling keys is redundant as >>> iteration over a dict iterates over its keys; but for subclasses or other >>> mappings, update prefers to use the keys method. >>> >>> The above paragraph may be inaccurate. Although the dict docstring >>> states that keys will be called if it exists, this does not seem to be >>> the case for dict subclasses. Bug or feature? >>> >> >> >>> print(dict.update.__doc__) >> D.update([E, ]**F) -> None. Update D from dict/iterable E and F. >> If E is present and has a .keys() method, then does: for k in E: D[k] = >> E[k] >> If E is present and lacks a .keys() method, then does: for k, v in E: >> D[k] = v >> In either case, this is followed by: for k in F: D[k] = F[k] >> >> It's actually pretty interesting... and misleading/wrongish. It never >> says that keys is *called*... in reality, it just checks for the "keys" >> method before deciding whether to proceed with PyDict_Merge or PyDict >> _MergeFromSeq2. It should really read more like: >> >> D.update([E, ]**F) -> None. Update D from dict/iterable E and F. >> If E is present, has a .keys() method, and is a subclass of dict, then >> does: for k in E: D[k] = E[k] >> If E is present, has a .keys() method, and is not a subclass of dict, >> then does: for k in E.keys(): D[k] = E[k] >> If E is present and lacks a .keys() method, then does: for k, v in E: >> D[k] = v >> In either case, this is followed by: for k in F: D[k] = F[k] >> >> Should our __sub__ behavior be the same (i.e., iterate for dict >> subclasses and objects without "keys()", otherwise call "keys()" and >> iterate over that)? __iadd__ calls into this logic already. It seems to be >> the most "natural" solution here, if we desire behavior analogous to >> "update". >> >> Brandt >> >> On Fri, Mar 1, 2019 at 8:26 AM Steven D'Aprano <st...@pearwood.info> >> wrote: >> >>> Attached is a draft PEP on adding + and - operators to dict for >>> discussion. >>> >>> This should probably go here: >>> >>> https://github.com/python/peps >>> >>> but due to technical difficulties at my end, I'm very limited in what I >>> can do on Github (at least for now). If there's anyone who would like to >>> co-author and/or help with the process, that will be appreciated. >>> >>> >>> -- >>> Steven >>> _______________________________________________ >>> Python-ideas mailing list >>> Python-ideas@python.org >>> https://mail.python.org/mailman/listinfo/python-ideas >>> Code of Conduct: http://python.org/psf/codeofconduct/ >>> >>
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