On Wed, Aug 09, 2017 at 12:06:37PM -0400, C W wrote: > Dear Python experts, > > What exactly does the three dots do? > > aList = ...
... is literal syntax for the Ellipsis singleton object. Ellipsis was added to the language at the express request of the numpy developers. Although numpy is a third-party project outside of the standard library, it is big enough and important enough that their requests carry a LOT of weight with the core Python devs. Other features Python has that were originally added at the request of numpy include: - extended slicing with two colons obj[a:b:c] - the @ operator used by numpy for matrix multiplication. I don't know what Ellipsis is used for by numpy, but now it makes a convenient pseudo-pass command: class X: ... def func(): ... > It's an ellipsis, a spot holder to later. But what data type is it: vector, > matrix? Its a singleton object. Think of it as a sibling to None and NotImplemented, but with optional funny syntactic sugar ... to refer to it. None is a special value used as "no such value", or nil or null; NotImplemented is a special value used by operator dunder methods like __add__ and __mul__ to mean "I can't handle this argument"; Ellipsis is a special value used by numpy to mean whatever it is that numpy uses it to me. -- Steve _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor