[Python-Dev] Extending tuple unpacking (original) (raw)

Ron Adam rrr at ronadam.com
Tue Oct 11 22:41:01 CEST 2005

Reinhold Birkenfeld wrote:

Greg Ewing wrote:

Guido van Rossum wrote:

BTW, what should [a, b, *rest] = (1, 2, 3, 4, 5) do? Should it set rest to (3, 4, 5) or to [3, 4, 5]? Whatever type is chosen, it should be the same type, always. The rhs could be any iterable, not just a tuple or a list. Making a special case of preserving one or two types doesn't seem worth it to me. I don't think that [a, b, c] = iterable is good style right now, so I'd say that [a, b, *rest] = iterable should be disallowed or be the same as with parentheses. It's not intuitive that rest could be a list here.

I wonder if something like the following would fulfill the need?

This divides a sequence at given index's by using an divider iterator on it.

class xlist(list): def div_at(self, *args): """ return a divided sequence """ return [x for x in self.div_iter(*args)] def div_iter(self, *args): """ return a sequence divider-iter """ s = None for n in args: yield self[s:n] s = n yield self[n:]

seq = xlist(range(10))

(a,b),rest = seq.div_at(2)

print a,b,rest # 0 1 [2, 3, 4, 5, 6, 7, 8, 9]

(a,b),c,(d,e),rest = seq.div_at(2,4,6)

print seq.div_at(2,4,6) # [[0, 1], [2, 3], [4, 5], [6, 7, 8, 9]] print a,b,c,d,e,rest # 0 1 [2, 3] 4 5 [6, 7, 8, 9]

This addresses the issue of repeating the name of the iterable.

Cheers, Ron

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