[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Got it
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[Python-ideas] Re: Add switch-case statements in Python

[Daniel Moisset]

I'm not sure if you're reading the right document, but PEP 634 refers to
636 in its second paragraph

On Tue, 4 May 2021, 19:56 Shreyan Avigyan, 
wrote:

> Ok. Now I'm able to understand. PEP 634 should have a reference to PEP 636
> or else it's pretty hard to understand because the syntax  section
> demonstrates PEG implementation of this.
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

This thread is closed therefore. (It was mistakenly opened due to 
misunderstanding.)
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Ooops...Didn't notice it. Anyway this thread is considered closed.
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Ok.
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[Python-ideas] Re: Add switch-case statements in Python

[Brandt Bucher]

It does, right at the top: https://www.python.org/dev/peps/pep-0634/#abstract
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Ok. Now I'm able to understand. PEP 634 should have a reference to PEP 636 or 
else it's pretty hard to understand because the syntax  section demonstrates 
PEG implementation of this.
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

I'm confused. PEP 634 is about switch statements in Python or PEG?
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[Python-ideas] Re: Add switch-case statements in Python

[David Lowry-Duda]

> Isn't PEP 643 for PEG grammar pattern matching? (I'm talking about 
> switch statements in Python)

I think you are referring to PEP 634, the one I linked to. I suggest you 
read it (and the other link I sent).

I copy from PEP 636, marked as a sort of "tutorial" for PEP 634:

```
A match statement takes an expression and compares its value to 
successive patterns given as one or more case blocks. This is 
superficially similar to a switch statement in C, Java or JavaScript 
(and many other languages), but much more powerful.

The simplest form compares a subject value against one or more literals:

def http_error(status):
match status:
case 400:
return "Bad request"
case 404:
return "Not found"
case 418:
return "I'm a teapot"
case _:
return "Something's wrong with the Internet"
```

- DLD
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[Python-ideas] Re: Add switch-case statements in Python

[David Lowry-Duda]

> Most of programming languages out there have switch-case statements. 
> Python doesn't have support for switch-case statements though. 
> switch-case statements can sometimes be nice and tidy and sometimes it 
> may be a horrible nightmare. But that also applies to if-elif-else 
> statements. It would be nice to have switch-case statements support in 
> python.

See the pattern-matching PEPs such as https://www.python.org/dev/peps/pep-0634/

In short, python soon will have a sort of switch statement, though the 
semantics will be a bit different and it is actually a form of pattern 
matching.

See also the notes on pattern mathing in 
https://docs.python.org/3.10/whatsnew/3.10.html

- DLD
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Sorry PEP 634 not PEP 643
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[Python-ideas] Re: Add switch-case statements in Python

[Shreyan Avigyan]

Isn't PEP 643 for PEG grammar pattern matching? (I'm talking about switch 
statements in Python)
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[Python-ideas] Re: Add switch-case statements in Python

[Antal Gábor]

How is this differs from PEP 634 
(https://docs.python.org/3.10/whatsnew/3.10.html#pep-634-structural-pattern-matching)? 



On 2021. 05. 04. 20:33, Shreyan Avigyan wrote:

Most of programming languages out there have switch-case statements. Python 
doesn't have support for switch-case statements though. switch-case statements 
can sometimes be nice and tidy and sometimes it may be a horrible nightmare. 
But that also applies to if-elif-else statements. It would be nice to have 
switch-case statements support in python.

Suggested syntax :-
---

switch expr:
 case expr2:
 case expr3:
 statements
 default:
 statements


How should it be implemented?
---

First of all this will require a new syntax. Second I suggest for comparing the 
case expr with switch expr, compare the pointers instead of objects for better 
performance. Usually if the ladder is represented using if-elif-else logic then 
it would be lower performance because we'll end up comparing objects not 
pointers.
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