I really like the PEP - it's a solid extension of the ideas introduced
by PEP 342.
The two changes I would suggest is that the PEP be made more explicit
regarding the fact that the try/finally block only enclose the yield
expression itself (i.e. no other parts of the containing statement) and
that the caching comment be updated with a list of specific semantic
elements that the caching should not affect.
For the first part, I would prefer if the example was changed to use
capitals for the variant non-keyword parts of the statement:
RESULT = yield from EXPR
And that it formally expanded to:
_i = iter(EXPR)
try:
_u = _i.next()
while 1:
try:
_v = yield _u
except Exception, _e:
_m = getattr(_i, 'throw', None)
if _m is not None:
_u = _m(_e)
else:
raise
else:
if _v is None:
_u = _i.next()
else:
_u = _i.send(_v)
except StopIteration, _e:
_expr_result = _e.value
finally:
_m = getattr(_i, 'close', None)
if _m is not None:
_m()
RESULT = _expr_result
I believe writing it that way would make it clearer that the scope of
the try/finally block doesn't include the assignment part of the statement.
For the second part, the specific semantics that I believe should be
noted as not changing even if an implementation chooses to cache the
bound methods are these:
- The "send" and "throw" methods of the subiterator should not be
retrieved if those methods are never called on the delegating generator
- If "send" is called on the delegating generator and the subiterator
has no "send" method, then an appropriate "AttributeError" should be
raised in the delegating generator
- If retrieving the "next", "send" or "throw" methods from the
subiterator results in an exception then the subiterator's "close"
method (if it has one) should still be called
Cheers,
Nick.
--
Nick Coghlan | [email protected] | Brisbane, Australia
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