On 2010-03-05 12:28 PM, Steven D'Aprano wrote:
On Fri, 05 Mar 2010 18:12:05 +0000, Arnaud Delobelle wrote:
l = range(10)
l
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
l[7::-1]
[7, 6, 5, 4, 3, 2, 1, 0]
[l[i] for i in range(7, -1, -1)]
[7, 6, 5, 4, 3, 2, 1, 0]
Where does the first -1 come from? Slices are supposed to have default
values of 0 and len(seq):
Rather, they have 0 and len(seq), respectively, when the step is positive, and
len(seq)-1 and -1 when the step is negative.
l[7::1]
[7, 8, 9]
[l[i] for i in range(7, len(l), 1)]
[7, 8, 9]
[l[i] for i in range(7, len(l), -1)]
[]
I don't believe the actual behaviour is documented anywhere.
True, I don't think it is.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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