How do I add an offset ot an IndexOf result in z3

Question

How do I add an offset to a value obtained from an IndexOf expression? That is, how do I do this?

> import z3
> s = 'hello'
> t = 'e'
> z3.simplify(z3.IndexOf(s, t, 0) + z3.IntVal(1))
z3.z3types.Z3Exception: Non-sequence passed as a sequence

I want to get the location after than of e.

On the other hand, switching the order works as expected

> z3.simplify(z3.IntVal(1) + z3.IndexOf(s, t, 0))
2

alias · Accepted Answer · 2019-02-28T05:17:40.120

4

You found a bug in z3py!

which reads:

    return SeqRef(Z3_mk_seq_index(s.ctx_ref(), s.as_ast(), substr.as_ast(), offset.as_ast()), s.ctx)

Instead, it should say:

    return ArithRef(Z3_mk_seq_index(s.ctx_ref(), s.as_ast(), substr.as_ast(), offset.as_ast()), s.ctx)

Once you make that change in your local-copy of z3.py, your program should work as is. Or you can wait till they release a fix.

edited Feb 28 '19 at 05:17

answered Feb 27 '19 at 21:17

alias

Thank you! Much appreciated. – Rahul Gopinath Feb 27 '19 at 21:28
By the way, do you know how to invoke the doctests on z3's python API? I don't see any docs on it. If possible, I want to contribute a fix and a test to make sure this gets fixed fast. – Rahul Gopinath Feb 28 '19 at 13:52
I believe they have some sort of a builtbot that runs all the tests upon a commit. I don't know how to run it locally though. See here: https://github.com/Z3Prover/z3test – alias Feb 28 '19 at 15:18

1 Answers1