En Sun, 18 Oct 2009 23:07:40 -0200, Raymond Hettinger <pyt...@rcn.com>
escribió:
[Raymond]
> If it really is a sequence (with len and getitem), you can write your
> own indexing iterator:
> def myslice(seq, start, stop, step):
> 'Allow forward or backwards iteration over a subslice'
> for i in range(start, stop, step):
> yield seq[i]
[StarWing]
Thank you. but it can't support negative index :-(
The negative index is handled by the line, "yield seq[i]".
s[-2:-5:-1] == ''.join(myslice(s, -2, -5, -1))
True
s[-5:-2:1] == ''.join(myslice(s, -5, -2, 1))
True
But not always:
py> s[10:-1:1]==''.join(myslice(s, 10, -1, 1))
False
py> s[-10:25:1]==''.join(myslice(s, -10, 25, 1))
False
You have to take the sequence length into account before computing the
range, not after.
--
Gabriel Genellina
--
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