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#### About the developer

python-constraint
290 Stars 57 Forks BSD 2-Clause "Simplified" License 78 Commits 21 Opened issues

#### Description

Constraint Solving Problem resolver for Python

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#### Contributors list

|Build Status| |Code Health| |Code Coverage|

# python-constraint

## Introduction

The Python constraint module offers solvers for

`Constraint Satisfaction 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, ...).

## Examples

Basics ~~~~~~

This interactive Python session demonstrates the module basic operation:

.. code-block:: python

```>>> 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 problem ~~~~~~~~~~~~~

The following example solves the classical Eight Rooks problem:

.. code-block:: python

```>>> 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()
>>> solutions
>>> solutions
[{0: 7, 1: 6, 2: 5, 3: 4, 4: 3, 5: 2, 6: 1, 7: 0},
{0: 7, 1: 6, 2: 5, 3: 4, 4: 3, 5: 2, 6: 0, 7: 1},
{0: 7, 1: 6, 2: 5, 3: 4, 4: 3, 5: 1, 6: 2, 7: 0},
{0: 7, 1: 6, 2: 5, 3: 4, 4: 3, 5: 1, 6: 0, 7: 2},
...
{0: 7, 1: 5, 2: 3, 3: 6, 4: 2, 5: 1, 6: 4, 7: 0},
{0: 7, 1: 5, 2: 3, 3: 6, 4: 1, 5: 2, 6: 0, 7: 4},
{0: 7, 1: 5, 2: 3, 3: 6, 4: 1, 5: 2, 6: 4, 7: 0},
{0: 7, 1: 5, 2: 3, 3: 6, 4: 1, 5: 4, 6: 2, 7: 0},
{0: 7, 1: 5, 2: 3, 3: 6, 4: 1, 5: 4, 6: 0, 7: 2},
...]
```

Magic squares ~~~~~~~~~~~~~

This example solves a 4x4 magic square:

.. code-block:: python

```>>> 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

.. role:: python(code) :language: python

Predefined constraint types currently available:

• :python:
`FunctionConstraint`
• :python:
`AllDifferentConstraint`
• :python:
`AllEqualConstraint`
• :python:
`ExactSumConstraint`
• :python:
`MaxSumConstraint`
• :python:
`MinSumConstraint`
• :python:
`InSetConstraint`
• :python:
`NotInSetConstraint`
• :python:
`SomeInSetConstraint`
• :python:
`SomeNotInSetConstraint`

## API documentation

Documentation for the module is available at: http://labix.org/doc/constraint/

## Download and install

.. code-block:: shell

```\$ pip install python-constraint
```

## Roadmap

This GitHub organization and repository is a global effort to help to maintain python-constraint which was written by Gustavo Niemeyer and originaly located at https://labix.org/python-constraint

• Create some unit tests - DONE
• Enable continuous integration - DONE
• Port to Python 3 (Python 2 being also supported) - DONE
• Respect Style Guide for Python Code (PEP8) - DONE
• Improve code coverage writting more unit tests - ToDo
• Move doc to Sphinx or MkDocs - https://readthedocs.org/ - ToDo

## Contact

But it's probably better to

`open an issue `
_.

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