Something probably not directly related, but since we started to talk about syntactic changes... I think what would be great to eventually have is some form of pattern matching. Essentially pattern matching could be just a "tagged" unpacking protocol. For example, something like this will simplify a common pattern with a sequence of if isinstance() branches: class Single(NamedTuple): x: int class Pair(NamedTuple): x: int y: int def func(arg: Union[Single, Pair]) -> int: whether arg: Single as a: return a + 2 Pair as a, b: return a * b else: return 0 The idea is that the expression before ``as`` is evaluated, then if ``arg`` is an instance of the result, then ``__unpack__`` is called on it. Then the resulting tuple is unpacked into the names a, b, etc. I think named tuples could provide the __unpack__, and especially it would be great for dataclasses to provide the __unpack__ method. (Maybe we can then call it __data__?) -- Ivan On 20 July 2017 at 11:39, Clément Pit-Claudel <cpitclaudel@gmail.com> wrote:
On 2017-07-20 11:30, Paul Moore wrote:
On 20 July 2017 at 10:15, Clément Pit-Claudel <cpitclaudel@gmail.com> wrote:
On 2017-07-20 11:02, Paul Moore wrote:
Also, what's the advantage of (x=1, y=2) over ntuple(x=1, y=2)? I.e., why does this need to be syntax instead of a library?
Agreed. Now that keyword argument dictionaries retain their order, there's no need for new syntax here. In fact, that's one of the key motivating reasons for the feature.
Isn't there a speed aspect? That is, doesn't the library approach require creating (and likely discarding) a dictionary every time a new ntuple is created? The syntax approach wouldn't need to do that.
I don't think anyone has suggested that the instance creation time penalty for namedtuple is the issue (it's the initial creation of the class that affects interpreter startup time), so it's not clear that we need to optimise that (at this stage)
Indeed, it's not clear we do. I was just offering a response to the original question, "what's the advantage of (x=1, y=2) over ntuple(x=1, y=2)?". _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/