[Python-Dev] PEP 334 - Simple Coroutines via SuspendIteration
Clark C. Evans
cce at clarkevans.com
Wed Sep 8 15:32:15 CEST 2004
On Wed, Sep 08, 2004 at 09:26:03AM -0400, Clark C. Evans wrote:
| On Wed, Sep 08, 2004 at 09:07:59AM -0400, Jp Calderone wrote:
| | def somefunc():
| | raise SuspendIteration()
| | return 'foo'
| | def genfunc():
| | yield somefunc()
| Interesting, but:
| - somefunc is a function, thus SuspendIteration() should
| terminate the function; raising an exception
| - somefunc is not a generator, so it cannot be yielded.
It's too early for me to be posting; scrap the nonsense in this second
point. I don't think this changes the suggestion below though.
| However, perhaps something like...
| def suspend(*args,**kwargs):
| raise SuspendIteration(*args,**kwargs)
| # never ever returns
| def myProducer():
| yeild "one"
| yield "two"
| Regardless, this is a side point. The authors of iterators that
| raise a SuspendIterator() will be low-level code, like a next()
| which reads the next block from a socket or row from a database
| query. In these cases, the class style iterator is sufficient.
| The real point, is that user-level generators, such as this example
| from the PEP (which is detailed as a class-based iterator), should
| transparently handle SuspendIteration() by passing it up the generator
| chain without killing the current scope.
| | def ListAlbums(cursor):
| | cursor.execute("SELECT title, artist FROM album")
| | yield '<html><body><table><tr><td>Title</td><td>Artist</td></tr>'
| | for (title, artist) in cursor:
| | yield '<tr><td>%s</td><td>%s</td></tr>' % (title, artist)
| | yield '</table></body></html>'
| For those who say that this iterator should be invalidated when
| cursor.next() raises SuspendIteration(), I point out that it is not
| invalided when cursor.next() raises StopIteration().
| Kind Regards,
| Clark C. Evans Prometheus Research, LLC.
| o office: +1.203.777.2550
| ~/ , mobile: +1.203.444.0557
| (( Prometheus Research: Transforming Data Into Knowledge
| \\ ,
| \/ - Research Exchange Database
| /\ - Survey & Assessment Technologies
| ` \ - Software Tools for Researchers
| ~ *
| Python-Dev mailing list
| Python-Dev at python.org
| Unsubscribe: http://mail.python.org/mailman/options/python-dev/cce%40clarkevans.com
Clark C. Evans Prometheus Research, LLC.
o office: +1.203.777.2550
~/ , mobile: +1.203.444.0557
(( Prometheus Research: Transforming Data Into Knowledge
\/ - Research Exchange Database
/\ - Survey & Assessment Technologies
` \ - Software Tools for Researchers
More information about the Python-Dev