Nick Coghlan <ncogh...@gmail.com> added the comment:

Given the direction of the python-dev thread, should we split this question 
into two issues?

Issue 1: a yield expression inside a comprehension changes the type of the 
expression result (returning a generator-iterator instead of the expected 
container type)

Issue 2: a yield expression inside a generator expression interacts weirdly 
with the genexp's implicit yield expression

I ask, as it seems to me that issue 1 can be addressed by wrapping the affected 
cases in an implicit 'yield from' expression, which will both fix the return 
type of the expression and turn the outer function into a generator (if it 
isn't one already). (I'm going to put together a proof-of-concept for that idea 
this weekend)

By contrast, the interaction between generator expressions and explicit yield 
expressions seems intrinsically confusing, so I'm not sure we can do any better 
than declaring it a syntax error to try to combine them.

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue10544>
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