[Python-Dev] switch-based programming in Python

[Thomas Wouters]

On Thu, Nov 08, 2001 at 04:45:07PM +0100, M.-A. Lemburg wrote:

> BTW, how did you get XS4ALL into funding the www.python.org traffic, if
> they don't heavily depend on Python ?

That's a complicated story. I'll be happy to explain it over a beer at IPC10
(if we both make it there ;P) but the short version is that XS4ALL is not an
ordinary company, we use a lot of opensource software, and my boss suggested
it. The traffic is peanuts, by the way, I think the more costly part is the
rackspace in our system room.

> I think that Skip's proposal would go a long way (sketching here
> a bit):

> It should be possible for the compiler to detect an if-elif-else
> construct which has the following signature:

> if x == 'first':...
> elif x == 'second':...
> else:...

[..]

> At runtime, the interpreter would check x for being one of the
> well-known immutable types (strings, unicode, numbers) and
> use the hash table for finding the right opcode snippet.

Hmm... I don't think this will have as much impact as you think. But testing
it like Martin suggested would be a good idea, and the compiler/interpreter
is a fun thing to play and experiment with.

[ About my switch proposal ]
> I think you missed some indents in your example. I added them again,
> removing the parens around x and tweaked the formatting a bit (also
> note the addition of a few breaks).

Actually, no, all but the parentheses were intentional. I don't like needing
the break (hence my comments about fallthrough) and I think the switch, case
and else should all be indented to the same level, just like 'if/elif/else'. 

>    def whatis(x):
>        switch x:
>            case 'one': 
>                print '1'
>                break

> Turns out that this look very Pythonic :-)

I like my version better, with the exception of the parentheses around 'x'
in 'switch(x):' :)

> Sure smells like PEP-time :-)

Aye, but lets do it while Guido is still on paternity leave so we at least
get to finish the proposal before it's -1'ed :)

-- 
Thomas Wouters <thomas@xs4all.net>

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