[Python-ideas] Revised**12 PEP on Yield-From
lists+python-ideas at jimpryor.net
Thu Apr 23 02:09:33 CEST 2009
On Wed, Apr 22, 2009 at 06:05:11PM +0200, Erik Groeneveld wrote:
> 2009/4/22 Jacob Holm <jh at improva.dk>:
> > In other words, the ValueError in the following example is swallowed
> > by close():
> >>>> def foo():
> > ... yield 'bar'
> > ... raise ValueError('baz')
> >>>> g = foo()
> >>>> g.next()
> > 'bar'
> >>>> g.close()
> I have the same code here, it does not raise an exception indeed.
> > This looks like close() doesn't actually behave as it should
> > according to PEP342. Interesting...
> From PEP342 (Thanks Jacob, for the reference):
> 4. Add a close() method for generator-iterators, which raises
> GeneratorExit at the point where the generator was paused. If
> the generator then raises StopIteration (by exiting normally,
> due to already being closed) or GeneratorExit (by not catching
> the exception), close() returns to its caller. If the
> yields a value, a RuntimeError is raised. If the generator
> raises any other exception, it is propagated to the caller.
> close() does nothing if the generator has already exited due to
> an exception or normal exit.
> > I would call that a bug.
> I agree with that.
I don't understand why you're both counting this as a bug. It looks like
exactly the behavior specified in PEP 342. When g.close() is evaluated,
a GeneratorExit is thrown to the suspended 'yield' expression in foo.
That exception is is not caught, so g terminates without executing the
rest of its code. The 'raise ValueError' line is never executed.
jim at jimpryor.net
More information about the Python-ideas