[MAL, on /F's complaints about
[for x in range(100): x*2]
]
> ...
> IMHO, the meaning of the differen parts is intuitively
> understandable from the fact that Python's standard "for"
> notation works in the same way.
>
> OTOH, the notation "x*2 for x in range(100)" looks strange to me
> and probably to others too, because it doesn't make clear what "x"
> really refers to until you read on... this is Python not Forth or
> Haskell !
The feature is taken from Haskell, which in turn adapted it from SETL. Both
follow the long-established ordering of mathematical set-builder notation,
where the *expression* is leftmost. It's the expression that's important,
not the incidental details of the iterators -- there's more than a century
of user experience behind that <0.6 wink>.
I'll note that everything "looks strange" the first time you see it. It's
more important that it feels right after you grasp it. That's the case
here! When I see
[x**2 for x in range(100)]
I (being a left-to-right reader) immediately grasp "ah, it's a list of
squares". Write it
[for x in range(100): x*2]
and it's simply harder to grasp (indeed, *that* "looks strange" to me -- it
looks like somebody started to write a "for" loop and made a typo).
In any case, this particular point was debated to death more than a year
ago, and Guido already Pronounced on it.
> ...
> Note that we could also extend the above by allowing multiple
> such constructs separated by commas:
>
> data = (1.3, 1.2, 1.1)
> l = [for x in data: 3*x,
> for x in data: x/10]
Sure, and we could write
u[...]
for Unicode lists too <wink>. I see no advantage in the above over the
simpler construct, i.e.
l = [3*x for x in data] + [x/10 for x in data]
except that it may be easier for a dirt-dumb implementation to optimize the
former.
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