On 22 November 2017 at 14:53, Serhiy Storchaka <storch...@gmail.com> wrote:
> 22.11.17 15:25, Ivan Levkivskyi пише: > >> I think this is indeed a problem.. For me the biggest surprise was that >> `yield` inside a comprehension does not turn a surrounding function into >> comprehension, see also >> https://stackoverflow.com/questions/29334054/why-am-i-gettin >> g-different-results-when-using-a-list-comprehension-with-coroutin >> >> In fact there is a b.p.o. issue for this https://bugs.python.org/issue1 >> 0544, it is assigned to me since July, but I was focused on other things >> recently. >> My plan was to restore the Python 2 semantics while still avoiding the >> leak of comprehension variable to the enclosing scope (the initial reason >> of introducing auxiliary "_make_list" function IIUC). >> So that: >> >> 1) g = [(yield i) for i in range(3)] outside a function will be a >> SyntaxError (yield outside a function) >> 2) g = [(yield i) for i in range(3)] inside a function will turn that >> enclosing function into generator. >> 3) accessing i after g = [(yield i) for i in range(3)] will give a >> NameError: name 'i' is not defined >> >> If you have time to work on this, then I will be glad if you take care of >> this issue, you can re-assign it. >> > > I have the same plan. I know how implement this for comprehensions, but > the tricky question is what to do with generator expressions? Ideally > > result = [expr for i in iterable] > > and > > result = list(expr for i in iterable) > > should have the same semantic. I.e. if expr is "(yield i)", this should > turn the enclosing function into a generator function, and fill the list > with values passed to the generator's .send(). I have no idea how implement > this. > > Yes, generator expressions are also currently problematic with `await`: >>> async def g(i): ... print(i) ... >>> async def f(): ... result = list(await g(i) for i in range(3)) ... print(result) ... >>> f().send(None) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 2, in f TypeError: 'async_generator' object is not iterable Maybe Yury can say something about this? -- Ivan
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