Creating slice notation from string

MRAB python at mrabarnett.plus.com
Thu Sep 3 00:11:17 CEST 2009


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]




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