On Fri, Feb 23, 2018 at 10:45 AM, Guido van Rossum <gu...@python.org> wrote:

> There are useful things you can only do with comprehensions if the second
> for-loop can use the variable in the first for-loop. E.g.
> [(i, j) for i in range(10) for j in range(i)]

indeed -- and that is fairly common use-case in nested for loops -- so good
to preserve this.

But I still think the original:

[g(y) for x in range(5) for y in [f(x)]]

Is always going to be confusing to read. Though I do agree that it's not
too bad when you unpack it into for loops:

In [89]: for x in range(5):
    ...:     for y in [f(x)]:
    ...:         l.append(g(y))

BTW, would it be even a tiny bit more efficient to use a tuple in the inner

[g(y) for x in range(5) for y in (f(x),)]



Christopher Barker, Ph.D.

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