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

[Ivan Levkivskyi]

On 23 November 2017 at 13:11, Paul Moore <p.f.moore at gmail.com> wrote:

> On 23 November 2017 at 12:01, Ivan Levkivskyi <levkivskyi at gmail.com>
> wrote:
>
> > "I don't use it, therefore it is not needed"  is a great argument,
> thanks.
> > Lets just forget about two SO questions and dozens people who up-voted
> it.
> > Do you use async comprehensions? If not, then we don't need them either.
>
> For those of us trying to keep up with the discussion who don't have
> time to chase the various references, and in the interest of keeping
> the discussion in one place, can you summarise the real-world use
> cases from the SO questions here? (I assume they are real world cases,
> and not just theoretical questions)
>

OK, here are the links:

https://stackoverflow.com/questions/45190729/differences-between-generator-comprehension-expressions
https://stackoverflow.com/questions/29334054/why-am-i-getting-different-results-when-using-a-list-comprehension-with-coroutin
https://bugs.python.org/issue10544
https://bugs.python.org/issue3267

In all four cases pattern is the same, people were trying to refactor
something like this:

def f():
    res = []
    for x in y:
        r = yield x
        res.append(r)
    return res

into something like this:

def f():
    return [(yield x) for x in y]

My understanding is that none of the case is _pressing_, since they all
start with a for-loop, but
following this logic comprehensions themselves are not needed. Nevertheless
people use them because they like it.
The problem in all four cases is that they got hard to debug problem, since
calling `f()` returns a generator,
just not the one they would expect.

--
Ivan
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