On 17 October 2016 at 21:22, Random832 <random832@fastmail.com> wrote:

No, it's not.

For a more concrete example:

[*range(x) for x in range(4)]
[0, 0, 1, 0, 1, 2]

There is simply no way to get there by using flatten(range(4)).

the equivalent flatten for that is:
flatten(range(x) for x in range(4)) ; flatten has no magic so will not replace a piece of code with two range calls (like your example) for code with one.

I see some mention that flatten does not cover all cases; but correct me if I'm wrong with this statement:

Any case of [*<exp1> for <vars> in <exp2>] could be replaced with flatten(<exp1> for <vars> in <exp2>). Where flatten is defined as 

def flatten(it):
    return [x for for subit in it for x in subit]

(there is a slight difference where I'm making flatten iterable instead of a list)

What perhaps was confusing is that in the case where <exp1> and <vars> are the same, you can also write flatten(<exp2>).

So, for me, this feature is something that could be covered with a (new) function with no new syntax required. All you have to learn is that instead of [*...] you use flatten(...)

Am I wrong? I keep reading people on both sides saying "flatten is not enough in all cases", and I can find a counterexample (even for 1 level flatten which is what I used here)

PS: or alternatively, flatten = lambda it: list(itertools.chain(it)) # :)
PPS: or if you prefer to work with iterators, flatten = itertools.chain

Daniel F. Moisset - UK Country Manager
Skype: @dmoisset