*-unpacking (Re: Fun with fancy slicing)

[David C. Fox]

Greg Ewing (using news.cis.dfn.de) wrote:
> Alex Martelli wrote:
> 
>> How sweet it would be to be able to unpack by coding:
>>     head, *tail = alist
> 
> 
> Indeed! I came across another use case for this
> recently, as well. I was trying to parse some
> command strings of the form
> 
>    command arg arg ...
> 
> where some commands had args and some didn't.
> I wanted to split the command off the front
> and keep the args for later processing once
> I'd decoded the command. My first attempt
> went something like
> 
>   command, args = cmdstring.split(" ", maxsplit = 1)
> 
> but this fails when there are no arguments,
> because the returned list has only one element
> in that case.
> 
> It would have been very nice to be able to
> simply say
> 
>   command, *args = cmdstring.split()
> 
> and get the command as a string and a
> list of 0 or more argument strings.
> 
> I really ought to write a PEP about this...
> 

In the mean time, it isn't too hard to write a function which does this:

     def first_rest(x):
         return x[0], x[1:]

     command, args = first_rest(cmdstring.split())

or, in one step

     def chop_word(s):
         return first_rest(s.split())

     command, args = chop_word(cmdstring)

David