On 16/08/2020 8:23 pm, Jean Abou Samra wrote:
Hi there,
As a poor user, I am extremely excited about the possibilities PEP 622
(structural pattern matching) opens. I'd like to ask a few questions.
OOI, what possibilities?
I'm genuinely interested know what problems PEP 622 would solve for you.
I hope these were not already answered in other threads, which it is hard to
follow given the amounts of information.
First, I'd like to know wether walrus patterns are encouraged as an expressive
way to explain the code in addition to comments, for example:
match number:
case exact := numbers.Rational():
...
case inexact:
...
Here we rename number depending on the case clause that was taken. Would this
be considered good practice? Maybe it'd be worth codifying in PEP 8 if PEP 622
is accepted?
A nit: how is the keywords module going to integrate soft keywords? Perhaps not
at all?
Also, I see potential for a caveat:
match number:
case int: # missing parentheses!
...
case float:
...
case Fraction:
...
In this case, if I understand the specification correctly, the first case will
always match, right? Maybe the interpreter could throw a SyntaxWarning when a
bare capture pattern (without a guard) is used as a pattern in any case clause
other than the last one? As far as I understand, this could possibly prevent
many of the mistakes in load/store that people have been rightfully complaining
about so far. It's merely a stronger measure than letting static checkers do
the work (since we don't all use these tools).
Finally, was as-based syntax considered as an alternative to walrus patterns, that is,
PATTERN as NAME instead of NAME := PATTERN, as we have in the try statement? Given the
extensive discussion, I guess it might have been rejected, so it could deserve a place
under "Rejected ideas" -- this holds for all the above too, which I'm sorry
about if it's dumb.
Best regards,
Jean Abou Samra
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