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

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At 02:10 PM 8/25/2005 -0500, Ian Bicking wrote:>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+5>>So 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()The initial next() will yield 0, not None.>  >>> s.send(1)>01>  >>> s.send(5)>16>  >>> s.send(1)>67>Is 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) == i>0 2 4 6 8The assert will fail on the first pass.  s.send(2) will == i+2, e.g.: >>> s = accum(0) >>> for i in s:...     if i>=10: break...     print i,...     assert s.send(2) == i+2...0 2 4 6 8

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