myth1 python-constraint-master # pythonPython 2.7.12 (default, Dec 17 2016, 17:32:09)[GCC 4.9.3] on linux2Type "help", "copyright", "credits" or "license" for more information.>>> from constraint import *>>> p = Problem()>>> p.addVariable('a', [-1,0,1])>>> p.addVariable('b', [-1,0,1])>>> p.addConstraint(ExactSumConstraint(0), ['a', 'b'])>>> print p.getSolutions()[{'a': 0, 'b': 0}]>>>