[Python-ideas] Revised**6 PEP on yield-from
dangyogi at gmail.com
Sun Feb 22 05:02:17 CET 2009
Greg Ewing wrote:
> * Any values sent to the delegating generator using ``send()``
> are passed directly to the iterator. If the sent value is None,
> the iterator's ``next()`` method is called. If the sent value is
> not None, the iterator's ``send()`` method is called if it has
> one, otherwise an exception is raised in the delegating generator.
Shouldn't this define which exception is raised?
Also, raising the exception within the delegating generator will (unless
caught there) finalize the generator. This may cause surprising results
if the caller catches the exception and tries to continue to use the
Intuitively, I would expect that the delegating generator would not see
this exception; as if the delegating generator itself lacked a send
method. The reasoning is that the error is with the caller and not the
delegating generator. Also, given that the send method may work while
the delegating generator is outside of any yield from, but not work
during a yield from; not raising the exception within the delegating
generator gives the caller a safe way to test the waters without
finalizing the delegating generator.
OTOH, this may be a reason to just translate send to next for non-None
values too??? Perhaps the justification in that case would be to think
of it like sending to a yield *statement* (which can't accept the sent
value) -- which is not an error in generators.
(Is it too late to change my vote for send(non-None) generating an
> 2. In a generator, the statement
> raise value
> is semantically equivalent to
> raise StopIteration(value)
Did you mean "return value" rather than "raise value" here?
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