On 07.02.2021 0:24, Paul Sokolovsky wrote:
Hello,
On Sun, 7 Feb 2021 00:00:41 +0300
Ivan Pozdeev via Python-Dev <python-dev@python.org> wrote:
Who said "__future__"?
Other people said __future__. And yet other said "it's ok the way it
is, it's better to have it like that then keep not having it". And yet
other said something else (multiple else's).
I said "3rd-party library". Independent from
the CPython project. Maybe even a few of them -- to try out
conflicting visions that emerged in the discussions.
Such libraries exist for decade(s). MacroPy is a venerable, well-known
macro-capabilities-for-Python solution, which offers a kind of pattern
matching: https://macropy3.readthedocs.io/en/latest/pattern.html .
There're a bunch of other, grep github.
https://github.com/MegaIng/syntax-extensions-pep634 specifically
advertises itself as pure-Python implementation of PEP634 (using a
newer macro library), though I'm not sure how well it's development.
It also of course represents the right way to develop Python - in
Python itself. Sadly, "C" in "CPython" is stuck too deep in many
minds...
Bottom line is however: given the decade(s) old history of pattern
matching in *Python* (usual warning: don't mix up Python and CPython!),
arguing that very resourceful attempt to add pattern matching to the
reference implementation (that's where *CPython* finally pops up),
should be flushed down the toilet and the Python community should be
brought back into decade-long waiting state without a reference
implementation for pattern matching - umm, suggesting that doesn't seem
to be very productive.
That's not the impression I got from looking through the discussiuon and the
PEP.
I don't see references to any of those existing implementations anywhere in the PEP as well as a summary of various existing approaches and
solutions, their pros and cons etc. which the proposal proper would derive its particulars from.
Both the PEPs and the discussion look like they are trying to write the
functionality completely from sctratch, by the seat of their pants.
And from how much discord there is about syntax and semantics, I conclude that these are far from being well-established and
practice-proven. So if the existing solutions really have a "decades-long history" as you claim, that history must be spectacularly
uneventful -- which suggests that the feature is either in low demand or was ultimately proven by practice to be inadequate for real-world use.
On 06.02.2021 23:58, Steve Holden wrote:
My suggestion that it be introduced via __future__ due to its
contentious nature met immediate resistance. No point going down
that road.
Kind regards,
Steve
On Sat, Feb 6, 2021 at 8:15 PM Ivan Pozdeev via Python-Dev
<python-dev@python.org <mailto:python-dev@python.org>> wrote:
With such a large new area of functionality that's at odds with
existing syntax and semantics and a lack of clear vision and
agreement, it sounds like this would be better first added as a
3rd-party library to let the syntax and semantics mature. (To allow
new syntax, it'll probably be parsing strings in that special
syntax.)
(At https://www.python.org/dev/peps/pep-0634/
<https://www.python.org/dev/peps/pep-0634/>, there's no indication
that this option was considered.)
[]
--
Regards,
Ivan
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