===================
 python-constraint
===================
:Author: Gustavo Niemeyer
:Contact: [email protected]
:Revision: $Rev$
:Date: $Date$

.. contents::


--------
Overview
--------

**python-constraint** [1]_ is a Python module offering solvers for
Constraint Solving Problems (CSPs) over finite domains in simple
and pure Python. CSP is class of problems which may be represented
in terms of variables (`a`, `b`, ...), domains (`a in [1, 2, 3]`, ...),
and constraints (`a < b`, ...).

.. [1] http://codespeak.net/~niemeyer/constraint/

--------
Examples
--------

Basic
-----

Here is a basic interactive example::
 
    >>> from constraint import *
    >>> problem = Problem()
    >>> problem.addVariable("a", [1,2,3])
    >>> problem.addVariable("b", [4,5,6])
    >>> problem.getSolutions()
    [{'a': 3, 'b': 6}, {'a': 3, 'b': 5}, {'a': 3, 'b': 4},
     {'a': 2, 'b': 6}, {'a': 2, 'b': 5}, {'a': 2, 'b': 4},
     {'a': 1, 'b': 6}, {'a': 1, 'b': 5}, {'a': 1, 'b': 4}]
    
    >>> problem.addConstraint(lambda a, b: a*2 == b,
                              ("a", "b"))
    >>> problem.getSolutions()
    [{'a': 3, 'b': 6}, {'a': 2, 'b': 4}]
    
    >>> problem = Problem()
    >>> problem.addVariables(["a", "b"], [1, 2, 3])
    >>> problem.addConstraint(AllDifferentConstraint())
    >>> problem.getSolutions()
    [{'a': 3, 'b': 2}, {'a': 3, 'b': 1}, {'a': 2, 'b': 3},
     {'a': 2, 'b': 1}, {'a': 1, 'b': 2}, {'a': 1, 'b': 3}]


Rooks
-----

Here is an example solving the classical rooks problem::

    problem = Problem()
    numpieces = 8
    cols = range(numpieces)
    rows = range(numpieces)
    problem.addVariables(cols, rows)
    for col1 in cols:
        for col2 in cols:
            if col1 < col2:
                problem.addConstraint(lambda row1, row2: row1 != row2,
                                      (col1, col2))
    solutions = problem.getSolutions()


Magic squares
-------------

And here is an example solving a 4x4 magic square::

    problem = Problem()
    problem.addVariables(range(0, 16), range(1, 16+1))
    problem.addConstraint(AllDifferentConstraint(), range(0, 16))
    problem.addConstraint(ExactSumConstraint(34), [0,5,10,15])
    problem.addConstraint(ExactSumConstraint(34), [3,6,9,12])
    for row in range(4):
        problem.addConstraint(ExactSumConstraint(34),
                              [row*4+i for i in range(4)])
    for col in range(4):
        problem.addConstraint(ExactSumConstraint(34),
                              [col+4*i for i in range(4)])
    solutions = problem.getSolutions()


--------
Features
--------

The following solvers are available:

- Backtracking solver
- Recursive backtracking solver
- Minimum conflicts solver

Predefined constraint types currently available:

- FunctionConstraint
- AllDifferentConstraint
- AllEqualConstraint
- ExactSumConstraint
- MaxSumConstraint
- MinSumConstraint
- InSetConstraint
- NotInSetConstraint
- SomeInSetConstraint
- SomeNotInSetConstraint


-------------
Documentation
-------------

There's documentation for the module at:

- http://codespeak.net/~niemeyer/constraint/doc/


--------
Download
--------

**python-constraint** may be found at the following
address:

- http://codespeak.net/~niemeyer/constraint/files/

---------------------
Subversion repository
---------------------

Available at:

- http://codespeak.net/svn/user/niemeyer/constraint/