On Sat, Oct 15, 2016 at 1:49 PM Steven D'Aprano <steve@pearwood.info> wrote:

...

And the transformation of *t for the items of t (I don't care if it is a
real transformation in the implementation, or only a fictional
transformation) cannot work in a list comp. Let's make the number of
items of t explicit so we don't have to worry about variable item
counts:

[*t for t in iterable] # t has three items
[a, b, c for (a, b, c) in iterable]

That's a syntax error. To avoid the syntax error, we need parentheses:

[(a, b, c) for (a, b, c) in iterable]

and that's a no-op.

You are confusing here two distinct roles of the parenthesis: disambiguation as in "(1 + 2) * 2", and tuple construction as in (1, 2, 3). This overload is the reason that (1) is not a 1-tuple and we must write (1,).

You may argue that this overloading causes confusion and make this construct hard to understand, but please be explicit about that; even if <1, 2,3 > was the syntax for tuples, the expansion was still

[(a, b, c) for (a, b, c) in iterable]

Since no tuple is constructed here.

Elazar