satispy 1.4

An interface to SAT solver tools (like minisat)

SATisPy

Satispy is a Python library that aims to be an interface to various SAT (boolean satisfiability) solver applications.

Supported solvers:

• Cadical
• CryptoMinisat
• Glucose
• Intel SAT Solver
• Lingeling
• MiniSAT
• PicoSAT
• Sat4j

Support for other solvers should be fairly easy to add as long as they accept the DIMACS CNF SAT format.

Installing

You can grab the current version from pypi:

$ sudo pip install satispy

Or you can download a copy from https://github.com/netom/satispy, and run

pip install .

in the directory.

You can run the tests found in the test folder by

./tests/run_tests.py.

All the solvers need to be installed to be able to run the tests.

How it works

You need the minisat SAT solver to be installed on your machine for this to work.

Let's see an example:

from satispy import Variable, Cnf
from satispy.solver import Minisat

v1 = Variable('v1')
v2 = Variable('v2')
v3 = Variable('v3')

exp = v1 & v2 | v3

solver = Minisat()

solution = solver.solve(exp)

if solution.success:
    print "Found a solution:"
    print v1, solution[v1]
    print v2, solution[v2]
    print v3, solution[v3]
else:
    print "The expression cannot be satisfied"

This program tries to satisfy the boolean expression

v1 & v2 | v3

You can make this true by assigning true to all variables for example, but there are other solutions too. This program finds a single arbitrary solution.

First, the program imports the various classes so we can build an expression and try to solve it.

SAT solvers expect their input to be in CNF, but we don't have to enter out expression as a CNF. The Cnf class takes care of the proper arranging of the boolean terms.

Expressions can be built by creating variables and gluing them together arbitrarily with boolean operators:

• NOT: - (unary)
• AND: &
• OR: |
• XOR: ^
• IMPLICATION >>

The solver class Minisat, Picosat, Sat4j, or Lingeling is used to solve the formula.

Note: these classes create temporary files, so they need write access to the system's temporary directory

The returned solution can be checked by reading the "success" boolean flag.

Then, the solution can be queried for variable assignments by using it like a dictionary. Note that Variable objects are used, not strings.

(This very example can be found in the examples directory)

Parsing Boolean expressions

It is also possible to create a Cnf object directly, without first creating Variable objects:

from satispy import CnfFromString
from satispy.solver import Minisat

exp, symbols = CnfFromString.create("v1 & v2 | v3")

solver = Minisat()

solution = solver.solve(exp)

if solution.success:
    print "Found a solution:"
    for symbol_name in symbols.keys():
        print "%s is %s" % (symbol_name, solution[symbols[symbol_name]])
else:
    print "The expression cannot be satisfied"