[Python-ideas] Yet Another Switch-Case Syntax Proposal

[Lucas Malor]

On 19 April 2014 05:12, Steven D'Aprano steve-at-pearwood.info |
python-ideas-at-python.org| <6hqclkasyt at sneakemail.com> wrote:

> In the case of your tarot
> example, it is *not* a violation of DRY, because the various elif lines
> are not *sources* of knowledge which may contradict each other. The
> worst that will happen is that if you change the variable name "tarot"
> to something else, your code will fail with a name error.


You could also use another existing variable. Anyway

if your
>
motive in introducing a switch/case statement is to DRY, I think you
> need a better motive.
>

I completely agree. I think the main good reason to introduce a switch
statement is that is more simple to use, when it can be used.


> @Skip Montanaro: yes, switch statement is used in C also for code
> > optimization. Frankly, I think this aspect is unimportant for CPython in
> > the present time.
>
> Then I think we're not going to agree on the use or need for switch.
>

To be clear: I'm not saying you can't improve the performance of a switch
statement, but IMHO currently Python has worse speed problems.


On 19 April 2014 07:11, Stephen J. Turnbull stephen-at-xemacs.org |
python-ideas-at-python.org| <85q573xayt at sneakemail.com> wrote:

> Skip Montanaro writes:
>
>  > In other languages, the semantics of the switch statement allow the
>  > compiler to generate more efficient code.  Instead of testing each
>  > branch of the if statement in succession looking for a match, you
>  > evaluate the switch expression once, then use it as an index into a
>  > jump table of some sort which points directly to the matching case
>  > label.
>
> Sure, but Python already has such a jump table: a function-valued
> hash.
>

Yes, I think it's more befitting than a switch.


On 19 April 2014 08:52, Bruce Leban bruce-at-leapyear.org |
python-ideas-at-python.org| <vajg1g2cqt at sneakemail.com> wrote:

> Here's a simple class that provides case like syntax. How would modifying
> the language be better than this?
>

I don't like the additional unneeded Case indentation. That's why I'm
proposing a syntax with switch on the same line with the first case.


I think case/elcase would be confusing as it would be unique to python and
> it's backwards -- the elcase keywords is used for the normal way that
> people use case statements while the case keyword implements the broken
> code that inexperienced C programmers frequently write.


This is the point. When I was a beginner I have not tried to code Python
directly, since it was an "exotic" language for me; so I read tutorials and
docs. In tutorial there will be an example with elcase, and if I have C
background I'll think "what damn is elcase"? And I'll read docs more
carefully.
And what if I read the code? If I don't know how switch statement works in
Python and I read a Python code with elcase, the result will be the same.
If I read an example without elcase, since it will work as a C switch
statement, there's no possibility of misunderstanding.

The problem with C switch is that you have to write break; at the end of
each case suite, and typically you forget to do it. With my proposal you
can't forget it if you know the syntax.
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