03-09-2009 o 00:11:17 MRAB <pyt...@mrabarnett.plus.com> wrote:
bvdp wrote:
I'm trying to NOT create a parser to do this .... and I'm sure that
it's easy if I could only see the light!
Is it possible to take an arbitrary string in the form "1:2", "1",
":-1", etc. and feed it to slice() and then apply the result to an
existing list?
For example, I have a normal python list. Let's say that x = [1,2,3,4]
and I have a string, call it "s', in the format "[2:3]". All I need to
do is to apply "s" to "x" just like python would do.
I can, of course, convert "x" to a list with split(), convert the 2
and 3 to ints, and then do something like: x[a:b] ... but I'd like
something more general. I think the answer is in slice() but I'm lost.
>>> x = [1,2,3,4]
>>> s = "[2:3]"
>>> # Using map.
>>> x[slice(*map(int, s.strip("[]").split(":")))]
[3]
>>> # Using a list comprehension.
>>> x[slice(*[int(i) for i in s.strip("[]").split(":")])]
[3]
Of course, you could also do something like this:
eval('x' + s)
or
eval(str(x) + s)
-- but it's worse: less secure (e.g. if s could be user-typed) and most
probably much more time-consuming (especially the latter).
Cheers,
*j
--
Jan Kaliszewski (zuo) <z...@chopin.edu.pl>
--
http://mail.python.org/mailman/listinfo/python-list
