permutations

Python library for instantiating and working with permutation collections that provide efficient implementations of all sequence methods (including random-access retrieval by index).

Purpose

This library provides a drop-in alternative to the built-in itertools.permutations function. This alternative implements the features of a Sequence, including the ability to access individual entries using their index (without iterating over all permutations up to that point).

Installation and Usage

This library is available as a package on PyPI:

python -m pip install permutations

The library can be imported in the usual ways:

import permutations
from permutations import permutations

Examples

The permutations class can be used in the same way as the built-in itertools.permutations function:

>>> list(permutations(range(3)))
[(0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0)]
>>> list(permutations(range(3), 2))
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]

However, in addition to acting as an Iterable containing a collection of permutations, an instance of permutations also acts as a Sequence. In particular, it supports retrieval of specific permutations by their index and its length can be determined without iterating over its elements:

>>> ps = permutations(range(5))
>>> ps[37]
(1, 3, 0, 4, 2)
>>> permutations(range(20))[7**20]
(0, 13, 9, 6, 14, 8, 17, 1, 5, 12, 15, 18, 11, 16, 10, 2, 3, 4, 19, 7)
>>> len(permutations(range(8))) == 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1
True

Development

All installation and development dependencies are fully specified in pyproject.toml. The project.optional-dependencies object is used to specify optional requirements for various development tasks. This makes it possible to specify additional options (such as docs, lint, and so on) when performing installation using pip:

python -m pip install .[docs,lint]

Documentation

The documentation can be generated automatically from the source files using Sphinx:

python -m pip install .[docs]
cd docs
sphinx-apidoc -f -E --templatedir=_templates -o _source .. && make html

Testing and Conventions

All unit tests are executed and their coverage is measured when using pytest (see the pyproject.toml file for configuration details):

python -m pip install .[test]
python -m pytest

Alternatively, all unit tests are included in the module itself and can be executed using doctest:

python src/permutations/permutations.py -v

Style conventions are enforced using Pylint:

python -m pip install .[lint]
python -m pylint src/permutations

Contributions

In order to contribute to the source code, open an issue or submit a pull request on the GitHub page for this library.

Versioning

The version number format for this library and the changes to the library associated with version number increments conform with Semantic Versioning 2.0.0.

Publishing

This library can be published as a package on PyPI by a package maintainer. First, install the dependencies required for packaging and publishing:

python -m pip install .[publish]

Ensure that the correct version number appears in pyproject.toml, and that any links in this README document to the Read the Docs documentation of this package (or its dependencies) have appropriate version numbers. Also ensure that the Read the Docs project for this library has an automation rule that activates and sets as the default all tagged versions. Create and push a tag for this version (replacing ?.?.? with the version number):

git tag ?.?.?
git push origin ?.?.?

Remove any old build/distribution files. Then, package the source into a distribution archive:

rm -rf build dist src/*.egg-info
python -m build --sdist --wheel .

Finally, upload the package distribution archive to PyPI:

python -m twine upload dist/*