On Fri, Jul 10, 2020, 9:16 AM Eric Nieuwland <eric.nieuwl...@gmail.com> wrote:
> > On 10 Jul 2020, at 01:51, Jim Baker <jim.ba...@python.org> wrote: > > ... > Explicit namespacing (if a constant) or using a guard (if a variable) > seems to be the right solution, as Ethan demonstrated earlier. No need for > . or ^ or \ or ... to disambiguate. Also it seems to me that structural > pattern matching will build on two common usages of namespaces for > constants: > > 1. Constants used from other modules are almost always used in the module > namespace. Eg, socket.AF_UNIX or signal.SIGTERM. > 2. New code often tends to use constants defined within an Enum namespace. > Hopefully we will see more of this convention in usage. > > (Very much an aside: Interestingly with the socket module we see both used > - it defines its constants with IntEnum and exports them traditionally. The > namespace specifics it uses with IntEnum._convert_ to make this happen -- > strictly speaking EnumMeta._convert, not documented, and a bit hard to > follow -- might be possibly debatable, but it works out quite well in > practice in providing backwards compatibility while continuing to work with > a C source of these constants.) > > >> This would also mean >> case Point(x=\x, y=\y): >> should be used to obtain x and y from the Point instance. >> > > This approach makes deeper nesting of the structure much more cumbersome, > I think. > > How to match Polygon(Point(x0,y0), Point(x1, y1), Point(x2, y2)) based on > its structure? > And Polygon(Point(x0,y0), p1, Point(x2, y2))? > > I'm just trying to describe what v2 of the PEP is trying to do and how it then corresponds to a reasonable usage model. Sorry for any confusion. So in your scenario above, Polygon and Point are used as class patterns ( https://www.python.org/dev/peps/pep-0622/#class-patterns). Consequently they are treated accordingly and have that nice structural pattern matching quality! Earlier I was discussing constant patterns ( https://www.python.org/dev/peps/pep-0622/#constant-value-patterns), which require they be namespaced in some way (a qualified name as it is described in the PEP). - Jim
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