What about where/let expression? [(y, y) for x in some_list if y < 0 where y = f(x)] On Sun, Jun 21, 2009 at 10:36 AM, Lie Ryan<lie.1296@gmail.com> wrote:
Ben Finney wrote:
Lie Ryan <lie.1296@gmail.com> writes:
Steven D'Aprano wrote: <snip>
The only case it doesn't cover is where the second filter depends on the value of x, and even that can be covered with a *tiny* bit more work:
gen = ((x, 3*x**2-5*x+4) for x in seq if x % 3 != 2) result = [y[1] for y in gen if -y[0] < y[1] < y[0]]
It requires no new syntax, no changes to the behaviour of list comps, no new meaning on "as", it's understandable and readable.
I think it would be more readable without index references, but instead using tuple unpacking::
gen = ((x, 3*x**2-5*x+4) for x in seq if x % 3 != 2) result = [b for (a, b) in gen if -a < b < a]
It can even be done as a single expression without (IMO) significantly affecting readability::
result = [ b for (a, b) in ((x, 3*x**2-5*x+4) for x in seq if x % 3 != 2) if -a < b < a]
IMHO, when a comprehension requires more than a single line, it should turn into explicit loop.
<snip>
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