[Python-Dev] Some pattern annoyance

2023-08-02 Thread Christian Tismer-Sperling 

Hi folks,

I just used Structural Pattern Matching quite intensively and I'm
pretty amazed of the new possibilities.

But see this code, trying to implement Mark Pilgrim's regex
algorithm for roman literals with SPM:

With constants, I can write

match seq:
case "M", "M", "M", "M", *r:
return 4 * 1000, r

But if I want to use abbreviations by assignment, this is no longer
possible, and I have to write something weird like:

M = "M"
match seq:
case a, b, c, d, *r if M == a == b == c == d:
return 4 * 1000, r

So what is missing seems to be a notion of const-ness, which
could be dynamically deduced. Am I missing something?

--
Christian Tismer-Sperling:^)   [email protected]
Software Consulting  : http://www.stackless.com/
Strandstraße 37  : https://github.com/PySide
24217 Schönberg  : GPG key -> 0xFB7BEE0E
phone +49 173 24 18 776  fax +49 (30) 700143-0023
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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Barry 


> On 2 Aug 2023, at 12:03, Christian Tismer-Sperling  
> wrote:
> 
> Hi folks,
> 
> I just used Structural Pattern Matching quite intensively and I'm
> pretty amazed of the new possibilities.
> 
> But see this code, trying to implement Mark Pilgrim's regex
> algorithm for roman literals with SPM:
> 
> With constants, I can write
> 
>match seq:
>case "M", "M", "M", "M", *r:
>return 4 * 1000, r
> 
> But if I want to use abbreviations by assignment, this is no longer
> possible, and I have to write something weird like:
> 
>M = "M"
>match seq:
>case a, b, c, d, *r if M == a == b == c == d:
>return 4 * 1000, r
> 
> So what is missing seems to be a notion of const-ness, which
> could be dynamically deduced. Am I missing something?

Try asking for help at https://discuss.python.org/
This list is not for help or ideas, also its basically dead.

Barry
> 
> -- 
> Christian Tismer-Sperling:^)   [email protected]
> Software Consulting  : http://www.stackless.com/
> Strandstraße 37  : https://github.com/PySide
> 24217 Schönberg  : GPG key -> 0xFB7BEE0E
> phone +49 173 24 18 776  fax +49 (30) 700143-0023
> ___
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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Christian Tismer-Sperling 

On 02.08.23 13:23, Barry wrote:



On 2 Aug 2023, at 12:03, Christian Tismer-Sperling 
 wrote:


Hi folks,

I just used Structural Pattern Matching quite intensively and I'm
pretty amazed of the new possibilities.

But see this code, trying to implement Mark Pilgrim's regex
algorithm for roman literals with SPM:

With constants, I can write

   match seq:
   case "M", "M", "M", "M", *r:
   return 4 * 1000, r

But if I want to use abbreviations by assignment, this is no longer
possible, and I have to write something weird like:

   M = "M"
   match seq:
   case a, b, c, d, *r if M == a == b == c == d:
   return 4 * 1000, r

So what is missing seems to be a notion of const-ness, which
could be dynamically deduced. Am I missing something?


Try asking for help at https://discuss.python.org/ 


This list is not for help or ideas, also its basically dead.



Thanks, Barry.
I thought this list would always stay intact as an alternatice
to the web things. How sad!

Cheers -- Chris

--
Christian Tismer-Sperling:^)   [email protected]
Software Consulting  : http://www.stackless.com/
Strandstraße 37  : https://github.com/PySide
24217 Schönberg  : GPG key -> 0xFB7BEE0E
phone +49 173 24 18 776  fax +49 (30) 700143-0023

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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Stephen J. Turnbull 
Christian Tismer-Sperling writes:

 > I thought this list would always stay intact as an alternatice
 > to the web things. How sad!

The list is alive.  You got an immediate answer, did you not?  It's
just that almost all of the people who are engaged with discussion
every day have found alternative platforms more productive.

Partly because that's where the other discussants are (the network
externality is undeniably powerful), and partly (I believe) because
effective use of email is a skill that requires effort to acquire.
Popular mail clients are designed to be popular, not to make that
expertise easy to acquire and exercise.  Clunky use of email makes
lists much less pleasant for everyone than they could be.

I guess that's sad (I am, after all, a GNU Mailman developer), but
it's reality.

Steve
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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Paul Moore 
On Wed, 2 Aug 2023 at 15:24, Stephen J. Turnbull <
[email protected]> wrote:

> Partly because that's where the other discussants are (the network
> externality is undeniably powerful), and partly (I believe) because
> effective use of email is a skill that requires effort to acquire.
> Popular mail clients are designed to be popular, not to make that
> expertise easy to acquire and exercise.  Clunky use of email makes
> lists much less pleasant for everyone than they could be.
>
> I guess that's sad (I am, after all, a GNU Mailman developer), but
> it's reality.
>

Personally, I'm sad because some people whose contributions I enjoy (you
being one of them :-)) didn't move to Discourse. But like you say, it's how
things are.

Christian - you can make named constants using class attributes (or an
enum):

class A:
M = "M"

match seq:
case A.M, A.M, A.M, A.M, *r:
return 4*1000, r

Basically, the "names are treated as variables to assign to" rule doesn't
apply to attributes.

I'm not sure how helpful that is (it's not particularly *shorter*) but I
think the idea was that most uses of named constants in a match statement
would be enums or module attributes. And compromises had to be made.

Cheers,
Paul
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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Christian Tismer-Sperling 

On 02.08.23 18:30, Paul Moore wrote:
On Wed, 2 Aug 2023 at 15:24, Stephen J. Turnbull 
> wrote:


Partly because that's where the other discussants are (the network
externality is undeniably powerful), and partly (I believe) because
effective use of email is a skill that requires effort to acquire.
Popular mail clients are designed to be popular, not to make that
expertise easy to acquire and exercise.  Clunky use of email makes
lists much less pleasant for everyone than they could be.

I guess that's sad (I am, after all, a GNU Mailman developer), but
it's reality.


Personally, I'm sad because some people whose contributions I enjoy (you 
being one of them :-)) didn't move to Discourse. But like you say, it's 
how things are.


Christian - you can make named constants using class attributes (or an 
enum):


class A:
     M = "M"

match seq:
     case A.M, A.M, A.M, A.M, *r:
         return 4*1000, r

Basically, the "names are treated as variables to assign to" rule 
doesn't apply to attributes.


I'm not sure how helpful that is (it's not particularly *shorter*) but I 
think the idea was that most uses of named constants in a match 
statement would be enums or module attributes. And compromises had to be 
made.


Cheers,
Paul


Thanks a lot, everybody!

I have tried a lot now, using classes which becomes more readable
but - funnily - slower! Using the clumsy if-guards felt slow but isn't.

Then I generated functions even, with everything as constants,
and now the SPM version in fact out-performs the regex slightly!

But at last, I found an even faster and correct algorithm
by a different approach, which ends now this story :)

Going to the Discourse tite, now.

Cheers -- Chris
--
Christian Tismer-Sperling:^)   [email protected]
Software Consulting  : http://www.stackless.com/
Strandstraße 37  : https://github.com/PySide
24217 Schönberg  : GPG key -> 0xFB7BEE0E
phone +49 173 24 18 776  fax +49 (30) 700143-0023

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[Python-Dev] Re: Some pattern annoyance

2023-08-02 Thread Steve Holden 
Hi Chris,

Nice to see you on the list.

While this is definitely off-topic, I trust I might be given license by the
list's few remaining readers to point out that the match-case construct is
for _structural_ pattern matching. As I wrote in the latest Nutshell:
"Resist the temptation to use match unless there is a need to analyse the
_structure_ of an object."

I don't believe it's accidental that match-case sequence patterns won't
match str, bytes or bytearrray objects - regexen are the tool already
optimised for that purpose, so it's quite impressive that you are
managing to approach the same level of performance!

Kind regards,
Steve


On Wed, 2 Aug 2023 at 18:26, Christian Tismer-Sperling 
wrote:

> On 02.08.23 18:30, Paul Moore wrote:
> > On Wed, 2 Aug 2023 at 15:24, Stephen J. Turnbull
> >  > > wrote:
> >
> > Partly because that's where the other discussants are (the network
> > externality is undeniably powerful), and partly (I believe) because
> > effective use of email is a skill that requires effort to acquire.
> > Popular mail clients are designed to be popular, not to make that
> > expertise easy to acquire and exercise.  Clunky use of email makes
> > lists much less pleasant for everyone than they could be.
> >
> > I guess that's sad (I am, after all, a GNU Mailman developer), but
> > it's reality.
> >
> >
> > Personally, I'm sad because some people whose contributions I enjoy (you
> > being one of them :-)) didn't move to Discourse. But like you say, it's
> > how things are.
> >
> > Christian - you can make named constants using class attributes (or an
> > enum):
> >
> > class A:
> >  M = "M"
> >
> > match seq:
> >  case A.M, A.M, A.M, A.M, *r:
> >  return 4*1000, r
> >
> > Basically, the "names are treated as variables to assign to" rule
> > doesn't apply to attributes.
> >
> > I'm not sure how helpful that is (it's not particularly *shorter*) but I
> > think the idea was that most uses of named constants in a match
> > statement would be enums or module attributes. And compromises had to be
> > made.
> >
> > Cheers,
> > Paul
>
> Thanks a lot, everybody!
>
> I have tried a lot now, using classes which becomes more readable
> but - funnily - slower! Using the clumsy if-guards felt slow but isn't.
>
> Then I generated functions even, with everything as constants,
> and now the SPM version in fact out-performs the regex slightly!
>
> But at last, I found an even faster and correct algorithm
> by a different approach, which ends now this story :)
>
> Going to the Discourse tite, now.
>
> Cheers -- Chris
> --
> Christian Tismer-Sperling:^)   [email protected]
> Software Consulting  : http://www.stackless.com/
> Strandstraße 37  : https://github.com/PySide
> 24217 Schönberg  : GPG key -> 0xFB7BEE0E
> phone +49 173 24 18 776  fax +49 (30) 700143-0023
>
> ___
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>
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