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[Python-Dev] PEP 342: simple example, closure alternative

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I was trying to translate a pattern that uses closures in a language like Scheme (where closed values can be written to) to generators using PEP 342, but I'm not clear exactly how it works; the examples in the PEP have different motivations.  Since I can't actually run these examples, perhaps someone could confirm or debug these:A closure based accumulator (using Scheme):(define (accum n)  (lambda (incr)   (set! n (+ n incr))   n))(define s (accum 0))(s 1) ; -> 1 == 0+1(s 5) ; -> 6 == 1+5So I thought the generator version might look like:def accum(n):     while 1:         incr = (yield n) or 0         n += incr >>> s = accum(0) >>> s.next() >>> s.send(1)0 >>> s.send(5)1 >>> s.send(1)6Is the order of the output correct?  Is there a better way to write accum, that makes it feel more like the closure-based version?Is this for loop correct? >>> s = accum(0) >>> for i in s:...     if i >= 10: break...     print i,...     assert s.send(2) == i0 2 4 6 8Hmm... maybe this would make it feel more closure-like:def closure_like(func):     def replacement(*args, **kw):         return ClosureLike(func(*args, **kw))     return replacementclass ClosureLike(object):     def __init__(self, iterator):         self.iterator = iterator         # I think this initial .next() is required, but I'm         # very confused on this point:         assert self.iterator.next() is None     def __call__(self, input):         assert self.iterator.send(input) is None         return self.iterator.next()@closure_likedef accum(n):     while 1:         # yields should always be in pairs, the first yield is input         # and the second yield is output.         incr = (yield) # this line is equivalent to (lambda (incr)...         n += incr      # equivalent to (set! ...)         yield n        # equivalent to n; this yield always returns None >>> s = accum(0) >>> s(1)1 >>> s(5)6Everything before the first (yield) is equivalent to the closed values between "(define (accum n)" and "(lambda" (for this example there's nothing there; I guess a more interesting example would have closed variables that were written to that were not function parameters).-- Ian Bicking  /ianb at colorstudy.com  /http://blog.ianbicking.org

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