New syntax for blocks

[Steven D'Aprano]

On Tue, 10 Nov 2009 20:13:21 -0800, Carl Banks wrote:

> On Nov 10, 7:12 pm, Steven D'Aprano
> <ste... at REMOVE.THIS.cybersource.com.au> wrote:
>> On Tue, 10 Nov 2009 12:45:13 -0800, Bearophile wrote:
>> > r:
>>
>> >> i think the following syntax would be quite beneficial to replace
>> >> some redundant "if's" in python code.
>>
>> >http://python.org/dev/peps/pep-3003/
>>
>> I knew it wouldn't take long for people to start responding to any
>> proposal with "don't bother, there's a moratorium".
>>
>> Of course in this case, the correct response would have been "don't
>> bother, it's a stupid idea, moratorium or no moratorium".
> 
> r didn't actually give a good example.  Here is case where it's actually
> useful.  (Pretend the regexps are too complicated to be parsed with
> string method.)
> 
> if re.match(r'go\s+(north|south|east|west)',cmd) as m:
>     hero.move(m.group(1))
> elif re.match(r'take\s+(\w+)',cmd) as m:
>     hero.pick_up(m.group(1))
> elif re.match(r'drop\s+(\w+)',cmd) as m:
>     here.put_Down(m.group(1))



This is where a helper function is good. You want a dispatcher:


COMMANDS = {
  r'go\s+(north|south|east|west)': hero.move, 
  r'take\s+(\w+)': hero.pick_up, 
  r'drop\s+(\w+)': here.put_Down,
  }

def dispatch(cmd):
    for regex in COMMANDS:
        m = re.match(regex, cmd)
        if m:
            COMMANDS[regex](m.group(1))
            break

dispatch(cmd)

If you need the regexes to be tested in a specific order, change the dict 
to an OrderedDict, or use a list of tuples and the obvious change to the 
for loop.



-- 
Steven