The proposal doesn't work well with type hints: atuple(a=1, b=2) and atuple(a="a", b="b") generates the same type.
Also, the automatic creation of a new type on-demand can lead to uncontrollable memory growth. On Thu, Mar 24, 2022 at 6:15 PM <mich...@michaelgreen.dev> wrote: > Back in early 2016 there was an idea submitted[1] by Joseph > Martinot-Lagarde in regard to anonymous namedtuples. The crux of the > submission was the idea of instantiating a namedtuple using only Python's > generic tuple syntax plus keyword arguments. At the time, the major > rebuttal against this idea however was that, since kwargs are an unordered > collection, it would be non-trivial to figure out a proper convention for > mapping an unordered collection onto an ordered one. > > Times have changed however, and with python3.6/3.7 we now have the > guarantee that dictionaries are insertion ordered. This means that by > extension keyword arguments are also ordered, and thus the major point of > contest against anonymous namedtuples is now moot. And as such I would like > to once again suggest anonymous namedtuples as a potential PEP. > > Proposal > ======= > The proposal ultimately is the same as before: > ``` > my_point = (x=12, y=16) > # (x=12, y=16) > my_point[0] > # 12 > ``` > > where kwargs can be passed to a tuple's instantiation [either via tuple() > or just ()], and these tuples would have all the same properties of a > namedtuple. > > A basic, pure-python implementation is actually quite trivial now given > that kwargs are ordered. Observe: > ``` > def atuple(**kwargs): > signature = " ".join(kwargs) > _type = atuple.__dict__.get(signature) > if not _type: > _type = namedtuple(atuple.__name__, signature) > atuple.__dict__[signature] = _type > return _type(**kwargs) > ``` > This has none of the problems suggested in the previous rebuttal. > > anonymous tuples of incorrect ordering raise the assertion error, as > expected: > > ``` > >>> assert atuple(x=12, y=16) == atuple(y=16, x=12) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AssertionError > ``` > > ...and by extension it preserves the users's specified ordering as given > by **kwargs. > ``` > >>> pt = atuple(r=3, theta=0.5, phi=0.25) > >>> pt > atuple(r=3, theta=0.5, phi=0.25) > ``` > > Given that this implementation caches the type by the keyword signature, > anonymous tuples of the same signature are recognized as the same type. > However, given differing values, they are not equal. > ``` > >>> type(atuple(x=1,y=2)) == type(atuple(x=1,y=2)) > True > >>> atuple(x=1,y=2) == atuple(x=1,y=3) > False > ``` > > This allows us to provide positional arguments to the construct, just like > regular namedtuples, and passing a mismatch throws an error as expected. > ``` > >>> pt = atuple(x=12, y=16) > >>> pt > atuple(x=12, y=16) > >>> type(pt)(1,2) > atuple(x=1, y=2) > >>> type(pt)(1,2,3) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: atuple.__new__() takes 3 positional arguments but 4 were given > ``` > > As we can see, the introduction of insertion-ordered dictionaries solves > all of the issues previously raised with regard to anonymous namedtuples. > > References: > [1] https://mail.python.org/pipermail/python-ideas/2016-April/039857.html > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/EUJTGE2VIHHMNJN574L5BEAS7ROSTYZL/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- Thanks, Andrew Svetlov
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