Examples for using sygus python api (#4822)

This PR adds examples for using the sygus python api.
The examples are obtained from the examples of the cpp sygus api.

1 files changed, 66 insertions, 0 deletions

diff --git a/examples/api/python/sygus-inv.py b/examples/api/python/sygus-inv.py
new file mode 100644
index 000000000..cb21e1849
--- /dev/null
+++ b/examples/api/python/sygus-inv.py
@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+#####################
+#! \file sygus-inv.py
+## \verbatim
+## Top contributors (to current version):
+##   Yoni Zohar
+## This file is part of the CVC4 project.
+## Copyright (c) 2009-2018 by the authors listed in the file AUTHORS
+## in the top-level source directory) and their institutional affiliations.
+## All rights reserved.  See the file COPYING in the top-level source
+## directory for licensing information.\endverbatim
+##
+## \brief A simple demonstration of the solving capabilities of the CVC4
+## sygus solver through the Python API. This is a direct
+## translation of sygus-inv.cpp .
+#####################
+
+import pycvc4
+from pycvc4 import kinds
+
+if __name__ == "__main__":
+  slv = pycvc4.Solver()
+
+  # required options
+  slv.setOption("lang", "sygus2")
+  slv.setOption("incremental", "false")
+
+  # set the logic
+  slv.setLogic("LIA")
+
+  integer = slv.getIntegerSort()
+  boolean = slv.getBooleanSort()
+
+  zero = slv.mkReal(0)
+  one = slv.mkReal(1)
+  ten = slv.mkReal(10)
+
+  # declare input variables for functions
+  x = slv.mkVar(integer, "x")
+  xp = slv.mkVar(integer, "xp")
+
+  # (ite (< x 10) (= xp (+ x 1)) (= xp x))
+  ite = slv.mkTerm(kinds.Ite,
+                        slv.mkTerm(kinds.Lt, x, ten),
+                        slv.mkTerm(kinds.Equal, xp, slv.mkTerm(kinds.Plus, x, one)),
+                        slv.mkTerm(kinds.Equal, xp, x))
+
+  # define the pre-conditions, transition relations, and post-conditions
+  pre_f = slv.defineFun("pre-f", {x}, boolean, slv.mkTerm(kinds.Equal, x, zero))
+  trans_f = slv.defineFun("trans-f", {x, xp}, boolean, ite)
+  post_f = slv.defineFun("post-f", {x}, boolean, slv.mkTerm(kinds.Leq, x, ten))
+
+  # declare the invariant-to-synthesize
+  inv_f = slv.synthInv("inv-f", {x})
+
+  slv.addSygusInvConstraint(inv_f, pre_f, trans_f, post_f)
+
+  # print solutions if available
+  if slv.checkSynth().isUnsat():
+    # Output should be equivalent to:
+    # (define-fun inv-f ((x Int)) Bool (not (>= x 11)))
+    slv.printSynthSolution()
+
+
+