Akihiro KAYAMA <[EMAIL PROTECTED]> wrote: > Thanks for your replies. > > But current Python generator specification requires me: > > def f1(): > for x in foo(f2, "foo"): yield x > for x in foo(f2, "foo"): yield x > # XXX v = ... (I don't know how to do this) > for x in foo(f2, "v=%s world" % v, "OK"): yield x > > I think it is not straitforward. Single level function which generator > impose is impractical for real use.
Not just impractical, there are plenty of situations where you simply cannot do that at all. Here's a greenlet example (from http://socal-piggies.org/presentations/grig/2005_07_21/): from py.magic import greenlet import xml.parsers.expat def send(arg): greenlet.getcurrent().parent.switch(arg) def start_element(name, attrs): send(('START', name, attrs)) def end_element(name): send(('END', name)) def char_data(data): data = data.strip() if data: send(('DATA', data)) def greenparse(xmldata): p = xml.parsers.expat.ParserCreate() p.StartElementHandler = start_element p.EndElementHandler = end_element p.CharacterDataHandler = char_data p.Parse(xmldata, 1) def iterxml(xmldata): g = greenlet(greenparse) data = g.switch(xmldata) while data is not None: yield data data = g.switch() if __name__ == "__main__": for data in iterxml("somexmldata"): # do something with data The greenlet here calls expat, but the 'yield' happens inside an expat callback. To get this to work you would need to rewrite expat to use its callback as a generator. Expat is coded in C, so you also need to find some way to get it to save the state of the C functions when it has yielded. I think this example should answer Arnaud's question ("In fact it is not clear to me at the moment what can be done (sensibly :) with the OP's Fiber class that cannot be achieved with the run() function I suggested.") Arnaud's run function cannot be used by anything which needs to save C stack state. > I am happy if I could use convenient coroutine features via standard > or simple extension library. py.magic.greenlet may be what I'm > looking for, but I wonder why this is named "magic" :-) I think it is called "magic" because it does something which is at first glance impossible: saving the C stack state as well as the Python stack. Possibly it does something underhand to achieve an impressive effect. I haven't looked at the implementation to see how it does it: creating threads and then scheduling them cooperatively would be one way but I expect it just switches the C stack around between different areas of memory. A long time ago I ported the BCPL coroutine library and there is one function in the middle (the one which does the stack switch) that definitely felt like magic. One interesting question raised by all this is whether those of us using Windows can usefully call Microsoft's Fiber functions through ctypes and get the benefit of coroutines without having to load any additional C extensions at all. -- http://mail.python.org/mailman/listinfo/python-list
