At 16:22 23.10.2003 -0700, Guido van Rossum wrote:
def tee(iterable): "Return two independent iterators from a single iterable" data = {} cnt = 0 def gen(next): global* cnt dpop = data.pop for i in count(): if i == cnt: item = data[i] = next() cnt += 1 else: item = dpop(i) yield item next = iter(iterable).next return (gen(next), gen(next))
which is IMO more readable.
it's a subtle piece of code. I wouldn't mind a more structured syntax with both the outer function declaring that is ok for some inner function to rebind some of its locals, and the inner function declaring that a local is coming from an outer scope:
def tee(iterable): "Return two independent iterators from a single iterable" data = {}
# cnt = 0 here would be ok
share cnt = 0: # the assignment is opt, # inner functions in the suite can rebind cnt def gen(next): use cnt # OR outer cnt dpop = data.pop for i in count(): if i == cnt: item = data[i] = next() cnt += 1 else: item = dpop(i) yield item
# cnt = 0 here would be ok
next = iter(iterable).next return (gen(next), gen(next))
yes it's heavy and unpythonic, but it makes very clear that something special is going on with cnt.
Might as well declare a class then. :-)
well, no, it's probably that I expect rebindable closed-over vars to be introduced but some kind of structured construct instead of the usual Python freeform. I think for this kind of situation I miss the Lisp-y 'let'. def counter(starval): share cnt = startval: def inc(i): use cnt cnt += i return cnt def dec(i) use cnt cnt -= i return cnt return inc,dec vs. def counter(starval): cnt = startval def inc(i): global cnt in counter cnt += i return cnt def dec(i) global cnt in counter cnt -= i return cnt return inc,dec vs. def counter(starval): class Counter: def __init__(self,startval): self.cnt = startval def inc(self,i): self.cnt += i return self.cnt def dec(self,i): self.cnt += i return self.cnt newcounter = Counter(startval) return newcounter.inc,newcounter.dec vs. (defun counter (startval) (let ((cnt startval)) (flet ((inc (i) (incf cnt i)) (dec (i) (decf cnt i))) (values #'inc #'dec)))) <wink>