compwa-python-constraint

Note

This is a packaging fork of python-constraint 1.4.0, maintained by the ComPWA project. It is published as compwa-python-constraint, but preserves the public constraint import package and the behavior of the upstream 1.4.0 solver.

Why this fork exists

The upstream 1.4.0 release on PyPI provides only a .tar.bz2 source distribution. PEP 625 standardized source distributions as gzip-compressed .tar.gz archives. In version 0.12.0, uv stopped accepting legacy source-distribution formats, including .tar.bz2, and recommends rebuilding affected packages as .tar.gz archives.

This fork makes that packaging-only update so projects can continue using the 1.4.0 implementation with current Python packaging tools. Its declarative pyproject.toml build produces:

• a pure-Python py3-none-any wheel, which installers can use without a local build step; and
• a standards-compliant .tar.gz source distribution as a fallback.

The distribution is versioned as 1.4.0.post1 to identify it as a downstream packaging revision. Solver changes continue to belong in the upstream project.

Introduction

The Python constraint module offers solvers for Constraint Satisfaction Problems (CSPs) over finite domains in simple and pure Python. A CSP can be represented in terms of variables, their possible domains, and constraints between them.

Examples

Basics

>>> 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

>>> 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

>>> problem = Problem()
>>> problem.addVariables(range(16), range(1, 17))
>>> problem.addConstraint(AllDifferentConstraint(), range(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 include:

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

Installation

python -m pip install compwa-python-constraint

The distribution name is compwa-python-constraint, while the import remains unchanged:

from constraint import Problem

Upstream project

python-constraint was written by Gustavo Niemeyer and is maintained at python-constraint/python-constraint. Please report solver bugs and propose behavioral changes upstream.

For packaging issues specific to this fork, use the ComPWA issue tracker.