[Python-Dev] Tricky way of of creating a generator via a comprehension expression

[Ethan Furman]

On 11/25/2017 04:20 PM, David Mertz wrote:
> On Sat, Nov 25, 2017 at 3:37 PM, Guido van Rossum wrote:

>> Maybe you didn't realize async/await don't need an event loop? Driving an async/await-based coroutine is just as
>> simple as driving a yield-from-based one (`await` does exactly the same thing as `yield from`).
>
> I realize I *can*, but it seems far from straightforward.  I guess this is really a python-list question or something,
> but what is the async/await spelling of something toy like:
>
>     In [1]: def fib():
>         ...:     a, b = 1, 1
>         ...:     while True:
>         ...:         yield a
>         ...:         a, b = b, a+b
>         ...:
>
>     In [2]: from itertools import takewhile
>
>     In [3]: list(takewhile(lambda x: x<200, fib()))
>     Out[3]: [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144]

>> Maybe the rest of the discussion should be about deprecation vs. SyntaxError in Python 3.7.
>
> I vote SyntaxError, of course. :-)

Given the recent thread about the difficulty of noticing DeprecationWarnings, I also vote SyntaxError.

On the other hand, if we have a change in 3.7 about the visibility of DeprecationWarnings, this would make an excellent 
test case.

--
~Ethan~