“Container” is a kind of pun, it’s something with a __contains__ method. The thing you’re looking for is “Collection”, which is the base for sequences, mappings and sets.
I also note that the discussion seems quite stuck. —Guido On Tue, Aug 24, 2021 at 21:55 Christopher Barker <python...@gmail.com> wrote: > It seems the conversation has confused two related concepts: > > 1) The default bool() implementation (Truthiness) -- this is what the OP > said was recommended by PEP 8: "For sequences, (strings, lists, tuples), > use the fact that empty sequences are false:" -- there is some debate about > that whether this is a good recommendation or not, but i don't think that's > the OPs point. Rather: > > 2) That there is no standard way to explicitly test containers for > "emptiness" - - there is only length, with the assumption that > len(something) == 0 or not len(something) is a good way to test for > emptiness. > > I still don't see why length is not perfectly adequate, but i wonder if > there are any "containers" i.e.things that could be empty, in the std lib > that don't support length. > > Looking in the ABCs, a Container is something that supports `in`, and a > Sized is something that supports len()-- so in theory, there could be a > Container that does not have a length. Are there any in the std lib? > > Perhaps the ABCs are instructive in another way here -- if we were to add > a __empty__ or some such dunder, what ABC would require it? Container? or > yet another one-method ABC? > > -CHB > > > On Tue, Aug 24, 2021 at 8:39 PM David Mertz, Ph.D. <david.me...@gmail.com> > wrote: > >> I wanted to do a survey of various "aggregates" in Python to see if any >> stand out as making the usual `if stuff: ...` troublesome. I wrote a >> little script at >> https://github.com/DavidMertz/LanguagePractice/blob/main/python/aggregates.py >> . >> >> I'm being deliberately vague about an "aggregate." It might not be a >> collection strictly speaking, but it is something that might seems to >> "contain" values in some sense. Basically, I think that standard library >> and built-in stuff behaves per PEP8. Some other libraries go their own >> way. I throw in a linked-list implementation I found on PyPI. I've never >> used it beyond this script; but per what it is, it cannot implement `len()` >> on O(1) (well, it *could* if it does extra bookkeeping; but then it's kinda >> a different thing). >> >> In NumPy land, the np.empty vs. np.zeros case is another oddball. On my >> system, my memory happened to have some prior value that wasn't zero; that >> could vary between runs, in principle. >> >> These are the results: >> >> Expr: '' | Value: '' >> Truth: False | Length: 0 >> Expr: list() | Value: [] >> Truth: False | Length: 0 >> Expr: tuple() | Value: () >> Truth: False | Length: 0 >> Expr: dict() | Value: {} >> Truth: False | Length: 0 >> Expr: set() | Value: set() >> Truth: False | Length: 0 >> Expr: bytearray() | Value: bytearray(b'') >> Truth: False | Length: 0 >> Expr: bytearray(1) | Value: bytearray(b'\x00') >> Truth: True | Length: 1 >> Expr: bytearray([0]) | Value: bytearray(b'\x00') >> Truth: True | Length: 1 >> Expr: array.array('i') | Value: array('i') >> Truth: False | Length: 0 >> Expr: array.array('i', []) | Value: array('i') >> Truth: False | Length: 0 >> Expr: Nothing() | Value: EmptyNamedTuple() >> Truth: False | Length: 0 >> Expr: deque() | Value: deque([]) >> Truth: False | Length: 0 >> Expr: deque([]) | Value: deque([]) >> Truth: False | Length: 0 >> Expr: ChainMap() | Value: ChainMap({}) >> Truth: False | Length: 0 >> Expr: queue.Queue() | Value: <queue.Queue object at 0x7f0940dd2190> >> Truth: True | Length: No length >> Expr: asyncio.Queue() | Value: <Queue at 0x7f0940dd2190 maxsize=0> >> Truth: True | Length: No length >> Expr: multiprocessing.Queue() | Value: <multiprocessing.queues.Queue >> object at 0x7f0940dd2190> >> Truth: True | Length: No length >> Expr: np.ndarray(1,) | Value: array([5.e-324]) >> Truth: True | Length: 1 >> Expr: np.ndarray((1,0)) | Value: array([], shape=(1, 0), dtype=float64) >> Truth: False | Length: 1 >> Expr: np.empty((1,)) | Value: array([5.e-324]) >> Truth: True | Length: 1 >> Expr: np.zeros((1,)) | Value: array([0.]) >> Truth: False | Length: 1 >> Expr: np.zeros((2,)) | Value: array([0., 0.]) >> Truth: No Truthiness | Length: 2 >> Expr: np.ones((1,)) | Value: array([1.]) >> Truth: True | Length: 1 >> Expr: np.ones((2,)) | Value: array([1., 1.]) >> Truth: No Truthiness | Length: 2 >> Expr: pd.Series() | Value: Series([], dtype: float64) >> Truth: No Truthiness | Length: 0 >> Expr: pd.DataFrame() | Value: Empty DataFrame >> Truth: No Truthiness | Length: 0 >> Expr: xr.DataArray() | Value: <xarray.DataArray ()> >> Truth: True | Length: No length >> Expr: linkedadt.LinkedList() | Value: <linkedadt.LinkedList object at >> 0x7f08d8d77f40> >> Truth: False | Length: 0 >> >> >> >> -- >> Keeping medicines from the bloodstreams of the sick; food >> from the bellies of the hungry; books from the hands of the >> uneducated; technology from the underdeveloped; and putting >> advocates of freedom in prisons. Intellectual property is >> to the 21st century what the slave trade was to the 16th. >> _______________________________________________ >> 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/XIQPNWDNRDGO3NOIY5KUHZ5CMR67TRWS/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > > > -- > Christopher Barker, PhD (Chris) > > Python Language Consulting > - Teaching > - Scientific Software Development > - Desktop GUI and Web Development > - wxPython, numpy, scipy, Cython > _______________________________________________ > 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/6QF7NPIB2ZODZWAR7VKVZJHSKADTORNG/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido (mobile)
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