Creating slice notation from string

[bvdp]

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.

Thanks.