[Python-ideas] Fwd: Fwd: Fwd: unpacking generalisations for list comprehension

[David Mertz]

On Mon, Oct 17, 2016 at 9:11 AM, Random832 <random832 at fastmail.com> wrote:

> Once again, this alleged simplicity relies on the chosen example "x for
> x" rather than "f(x) for x" - this one doesn't even put the use of
> flatten in the right place to be generalized to the more complex cases.
> You'd need list(flatten(f(x) for x in iterable))
>

What you're saying is EXACTLY 180 deg reversed from the truth.  It's
*precisely* because it doesn't need the extra complication that `flatten()`
is more flexible and powerful.  I have no idea what your example is meant
to do, but the actual correspondence is:

  [f(x) for x in flatten(it)]

Under my proposed "more flexible recursion levels" idea, it could even be:

  [f(x) for x in flatten(it, levels=3)]

There would simply be NO WAY to get that out of the * comprehension syntax
at all.  But a decent flatten() function gets all the flexibility.


> Honestly, it goes beyond just being "wrong". The repeated refusal to
> even acknowledge any equivalence between [...x... for x in [a, b, c]]
> and [...a..., ...b..., ...c...] truly makes it difficult for me to
> accept some people's _sincerity_.
>

I am absolutely sincere in disliking and finding hard-to-teach this novel
use of * in comprehensions.

Yours, David...

P.S. It's very artificial to assume user are unable to use 'from itertools
import chain' to try to make chain() seem more cumbersome than it is.
Likewise, I would like flatten() in itertools, but I assume the usual
pattern would be importing the function itself.

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