> > 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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