On 22 November 2017 at 16:08, Ivan Levkivskyi
On 22 November 2017 at 16:56, Yury Selivanov
wrote: On Wed, Nov 22, 2017 at 10:10 AM, Ivan Levkivskyi
wrote: On 22 November 2017 at 15:47, Paul Moore
wrote: [...] I'm all for prohibiting using 'yield' expression in generator expressions or comprehensions. The semantics is way to hard to understand and hence be of any value. Making 'await' a SyntaxError is absolutely not an option. Async generator expressions are a shorthand syntax for defining asynchronous generators (PEP 525), and it's already being used in the wild.
OK, makes sense, so it looks like we may have the following plan:
- fix `yield` in comprehensions
I'm still not clear what "fix" would actually mean, but you propose clarifying the docs below, so I assume it means "according to whatever the updated docs say"...
- update PEP 530 and docs re generator expressions vs comprehensions
Docs more importantly than PEP IMO. And are you implying that there's a difference between generator expressions and comprehensions? I thought both were intended to behave as if expanded to a function containing nested for loops? Nothing said in this thread so far (about semantics, as opposed to about current behaviour) implies there's a deliberate difference.
- make `yield` in generator expressions a SyntaxError
That contradicts the suggestion that generator expressions are equivalent to the expanded function definition we saw before.
If everyone agrees, then I propose to open a separate issue on b.p.o. to coordinate the efforts.
I agree it needs clarifying. Not sure I agree with your proposed semantics, but I guess that can wait for when we have a concrete doc change proposal. Paul