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) >0 1 > >>> s.send(5) >1 6 > >>> s.send(1) >6 7 >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 8 The 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 _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
