This kind of low level impl. where suspension points are known at runtime only,
cannot be implemented in jython
(at least not in a non costly and reasonable way).
Jython codebase is likely to just allow generators with suspension points known
at compilation time.
regards.
----- Original Message -----
From: Neil Schemenauer <nas@arctrix.com>
To: <python-dev@python.org>
Sent: Sunday, March 18, 2001 3:17 AM
Subject: [Python-Dev] Simple generators, round 2
> I've got a different implementation. There are no new keywords
> and its simpler to wrap a high level interface around the low
> interface.
>
> http://arctrix.com/nas/python/generator2.diff
>
> What the patch does:
>
> Split the big for loop and switch statement out of eval_code2
> into PyEval_EvalFrame.
>
> Add a new "why" flag for ceval, WHY_SUSPEND. It is similar to
> WHY_RETURN except that the frame value stack and the block stack
> are not touched. The frame is also marked resumable before
> returning (f_stackbottom != NULL).
>
> Add two new methods to frame objects, suspend and resume.
> suspend takes one argument which gets attached to the frame
> (f_suspendvalue). This tells ceval to suspend as soon as control
> gets back to this frame. resume, strangely enough, resumes a
> suspended frame. Execution continues at the point it was
> suspended. This is done by calling PyEval_EvalFrame on the frame
> object.
>
> Make frame_dealloc clean up the stack and decref f_suspendvalue
> if it exists.
>
> There are probably still bugs and it slows down ceval too much
> but otherwise things are looking good. Here are some examples
> (the're a little long and but illustrative). Low level
> interface, similar to my last example:
>
> # print 0 to 999
> import sys
>
> def g():
> for n in range(1000):
> f = sys._getframe()
> f.suspend((n, f))
> return None, None
>
> n, frame = g()
> while frame:
> print n
> n, frame = frame.resume()
>
> Let's build something easier to use:
>
> # Generator.py
> import sys
>
> class Generator:
> def __init__(self):
> self.frame = sys._getframe(1)
> self.frame.suspend(self)
>
> def suspend(self, value):
> self.frame.suspend(value)
>
> def end(self):
> raise IndexError
>
> def __getitem__(self, i):
> # fake indices suck, need iterators
> return self.frame.resume()
>
> Now let's try Guido's pi example now:
>
> # Prints out the frist 100 digits of pi
> from Generator import Generator
>
> def pi():
> g = Generator()
> k, a, b, a1, b1 = 2L, 4L, 1L, 12L, 4L
> while 1:
> # Next approximation
> p, q, k = k*k, 2L*k+1L, k+1L
> a, b, a1, b1 = a1, b1, p*a+q*a1, p*b+q*b1
> # Print common digits
> d, d1 = a/b, a1/b1
> while d == d1:
> g.suspend(int(d))
> a, a1 = 10L*(a%b), 10L*(a1%b1)
> d, d1 = a/b, a1/b1
>
> def test():
> pi_digits = pi()
> for i in range(100):
> print pi_digits[i],
>
> if __name__ == "__main__":
> test()
>
> Some tree traversals:
>
> from types import TupleType
> from Generator import Generator
>
> # (A - B) + C * (E/F)
> expr = ("+",
> ("-", "A", "B"),
> ("*", "C",
> ("/", "E", "F")))
>
> def postorder(node):
> g = Generator()
> if isinstance(node, TupleType):
> value, left, right = node
> for child in postorder(left):
> g.suspend(child)
> for child in postorder(right):
> g.suspend(child)
> g.suspend(value)
> else:
> g.suspend(node)
> g.end()
>
> print "postorder:",
> for node in postorder(expr):
> print node,
> print
>
> This prints:
>
> postorder: A B - C E F / * +
>
> Cheers,
>
> Neil
>
> _______________________________________________
> Python-Dev mailing list
> Python-Dev@python.org
> http://mail.python.org/mailman/listinfo/python-dev
>
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