A collection of design patterns/idioms in Python

Overview

python-patterns

A collection of design patterns and idioms in Python.

Current Patterns

Creational Patterns:

Pattern Description
abstract_factory use a generic function with specific factories
borg a singleton with shared-state among instances
builder instead of using multiple constructors, builder object receives parameters and returns constructed objects
factory delegate a specialized function/method to create instances
lazy_evaluation lazily-evaluated property pattern in Python
pool preinstantiate and maintain a group of instances of the same type
prototype use a factory and clones of a prototype for new instances (if instantiation is expensive)

Structural Patterns:

Pattern Description
3-tier data<->business logic<->presentation separation (strict relationships)
adapter adapt one interface to another using a white-list
bridge a client-provider middleman to soften interface changes
composite lets clients treat individual objects and compositions uniformly
decorator wrap functionality with other functionality in order to affect outputs
facade use one class as an API to a number of others
flyweight transparently reuse existing instances of objects with similar/identical state
front_controller single handler requests coming to the application
mvc model<->view<->controller (non-strict relationships)
proxy an object funnels operations to something else

Behavioral Patterns:

Pattern Description
chain_of_responsibility apply a chain of successive handlers to try and process the data
catalog general methods will call different specialized methods based on construction parameter
chaining_method continue callback next object method
command bundle a command and arguments to call later
iterator traverse a container and access the container's elements
iterator (alt. impl.) traverse a container and access the container's elements
mediator an object that knows how to connect other objects and act as a proxy
memento generate an opaque token that can be used to go back to a previous state
observer provide a callback for notification of events/changes to data
publish_subscribe a source syndicates events/data to 0+ registered listeners
registry keep track of all subclasses of a given class
specification business rules can be recombined by chaining the business rules together using boolean logic
state logic is organized into a discrete number of potential states and the next state that can be transitioned to
strategy selectable operations over the same data
template an object imposes a structure but takes pluggable components
visitor invoke a callback for all items of a collection

Design for Testability Patterns:

Pattern Description
dependency_injection 3 variants of dependency injection

Fundamental Patterns:

Pattern Description
delegation_pattern an object handles a request by delegating to a second object (the delegate)

Others:

Pattern Description
blackboard architectural model, assemble different sub-system knowledge to build a solution, AI approach - non gang of four pattern
graph_search graphing algorithms - non gang of four pattern
hsm hierarchical state machine - non gang of four pattern

Videos

Design Patterns in Python by Peter Ullrich

Sebastian Buczyński - Why you don't need design patterns in Python?

You Don't Need That!

Pluggable Libs Through Design Patterns

Contributing

When an implementation is added or modified, please review the following guidelines:

Output

All files with example patterns have ### OUTPUT ### section at the bottom (migration to OUTPUT = """...""" is in progress).

Run append_output.sh (e.g. ./append_output.sh borg.py) to generate/update it.

Docstrings

Add module level description in form of a docstring with links to corresponding references or other useful information.

Add "Examples in Python ecosystem" section if you know some. It shows how patterns could be applied to real-world problems.

facade.py has a good example of detailed description, but sometimes the shorter one as in template.py would suffice.

In some cases class-level docstring with doctest would also help (see adapter.py) but readable OUTPUT section is much better.

Python 2 compatibility

To see Python 2 compatible versions of some patterns please check-out the legacy tag.

Update README

When everything else is done - update corresponding part of README.

Travis CI

Please run tox or tox -e ci37 before submitting a patch to be sure your changes will pass CI.

You can also run flake8 or pytest commands manually. Examples can be found in tox.ini.

Contributing via issue triage Open Source Helpers

You can triage issues and pull requests which may include reproducing bug reports or asking for vital information, such as version numbers or reproduction instructions. If you would like to start triaging issues, one easy way to get started is to subscribe to python-patterns on CodeTriage.

Owner
Sakis Kasampalis
I like Programming and I enjoy writing code in pragmatic languages, without being dogmatic about them. My principle is to use the right tool for the job
Sakis Kasampalis
Fedlearn algorithm toolkit for researchers

Fedlearn algorithm toolkit for researchers

89 Nov 14, 2022
This is a Python implementation of the HMRF algorithm on networks with categorial variables.

Salad Salad is an Open Source Python library to segment tissues into different biologically relevant regions based on Hidden Markov Random Fields. The

1 Nov 16, 2021
QDax is a tool to accelerate Quality-Diveristy (QD) algorithms through hardware accelerators and massive parallelism

QDax: Accelerated Quality-Diversity QDax is a tool to accelerate Quality-Diveristy (QD) algorithms through hardware accelerators and massive paralleli

Adaptive and Intelligent Robotics Lab 183 Dec 30, 2022
Sign data using symmetric-key algorithm encryption.

Sign data using symmetric-key algorithm encryption. Validate signed data and identify possible validation errors. Uses sha-(1, 224, 256, 385 and 512)/hmac for signature encryption. Custom hash algori

Artur Barseghyan 39 Jun 10, 2022
FLIght SCheduling OPTimization - a simple optimization library for flight scheduling and related problems in the discrete domain

Fliscopt FLIght SCheduling OPTimization 🛫 or fliscopt is a simple optimization library for flight scheduling and related problems in the discrete dom

33 Dec 17, 2022
Using A * search algorithm and GBFS search algorithm to solve the Romanian problem

Romanian-problem-using-Astar-and-GBFS Using A * search algorithm and GBFS search algorithm to solve the Romanian problem Romanian problem: The agent i

Mahdi Hassanzadeh 6 Nov 22, 2022
A Python program to easily solve the n-queens problem using min-conflicts algorithm

QueensProblem A program to easily solve the n-queens problem using min-conflicts algorithm Performances estimated with a sample of 1000 different rand

0 Oct 21, 2022
This application solves sudoku puzzles using a backtracking recursive algorithm

This application solves sudoku puzzles using a backtracking recursive algorithm. The user interface is coded with Pygame to allow users to easily input puzzles.

Glenda T 0 May 17, 2022
A fast python implementation of the SimHash algorithm.

This Python package provides hashing algorithms for computing cohort ids of users based on their browsing history. As such, it may be used to compute cohort ids of users following Google's Federated

Hybrid Theory 19 Dec 15, 2022
A Python Package for Portfolio Optimization using the Critical Line Algorithm

A Python Package for Portfolio Optimization using the Critical Line Algorithm

19 Oct 11, 2022
A Python project for optimizing the 8 Queens Puzzle using the Genetic Algorithm implemented in PyGAD.

8QueensGenetic A Python project for optimizing the 8 Queens Puzzle using the Genetic Algorithm implemented in PyGAD. The project uses the Kivy cross-p

Ahmed Gad 16 Nov 13, 2022
Path tracing obj - (taichi course final project) a path tracing renderer that can import and render obj files

Path tracing obj - (taichi course final project) a path tracing renderer that can import and render obj files

5 Sep 10, 2022
8-puzzle-solver with UCS, ILS, IDA* algorithm

Eight Puzzle 8-puzzle-solver with UCS, ILS, IDA* algorithm pre-usage requirements python3 python3-pip virtualenv prepare enviroment virtualenv -p pyth

Mohsen Arzani 4 Sep 22, 2021
This project is an implementation of a simple K-means algorithm

Simple-Kmeans-Clustering-Algorithm Abstract K-means is a centroid-based algorithm, or a distance-based algorithm, where we calculate the distances to

Saman Khamesian 7 Aug 09, 2022
Machine Learning algorithms implementation.

Machine Learning Algorithms Machine Learning algorithms implementation. What can I find here? ML Algorithms KNN K-Means-Clustering SVM (MultiClass) Pe

David Levin 1 Dec 10, 2021
Exact algorithm for computing two-sided statistical tolerance intervals under a normal distribution assumption using Python.

norm-tol-int Exact algorithm for computing two-sided statistical tolerance intervals under a normal distribution assumption using Python. Methods The

Jed Ludlow 1 Jan 06, 2022
Python Sorted Container Types: Sorted List, Sorted Dict, and Sorted Set

Python Sorted Containers Sorted Containers is an Apache2 licensed sorted collections library, written in pure-Python, and fast as C-extensions. Python

Grant Jenks 2.8k Jan 04, 2023
Exam Schedule Generator using Genetic Algorithm

Exam Schedule Generator using Genetic Algorithm Requirements Use any kind of crossover Choose any justifiable rate of mutation Use roulette wheel sele

Sana Khan 1 Jan 12, 2022
Genius Square puzzle solver in Python

Genius Square puzzle solver in Python

James 3 Dec 15, 2022
Distributed Grid Descent: an algorithm for hyperparameter tuning guided by Bayesian inference, designed to run on multiple processes and potentially many machines with no central point of control

Distributed Grid Descent: an algorithm for hyperparameter tuning guided by Bayesian inference, designed to run on multiple processes and potentially many machines with no central point of control.

Martin 1 Jan 01, 2022