Popular Python recipes tagged "oop"

Emulating super() in Python 3.x using Python 2.7 (Python)

2016-07-31T04:03:29-07:00

Python recipe 580694 by sunqingyao (beginner, descriptor, metaclass, oop, python2).

Depending on the name of the first argument, self.__sup or cls.__sup behaves like super() in Python 3, while this code is written in Python 2.7.

It works for both ordinary methods and class methods(static methods don't use super()). See my code for detailed examples:

Python method chaining examples (Python)

2016-02-25T19:40:33-08:00

Python recipe 580616 by Vasudev Ram (chaining, methods, object, oop, python).

This recipe shows a few examples of doing method chaining in Python.

Wrap a a file-like object in another that calls a user callback whenever read() is called on it. (Python)

2013-09-25T01:54:53-07:00

Python recipe 578674 by Martin Miller (callback, file, oop, progress, upload).

Wraps a file-like object in another, but also calls a user callback with the number of bytes read whenever its read() method is called. Used for tracking upload progress, for example for a progress bar in a UI application.

Observer Pattern (Python)

2013-03-09T10:03:10-08:00

Python recipe 578484 by Mauro B. Bianc (cascade, observer, oop, pattern, patterns, setattr, __setattr__). Revision 2.

This is a Python implementation of the observer pattern described by Gamma et. al. It defines a one-to many dependency between objects so that when one object changes state, all its dependents (i.e. observers) are notified and updated automatically.

My adaptation gets rid of the need to use specific functions to set the data (and to call Notify) and allows you to be notified for ANY attribute you set. It is possible to specify a list of attributes which should not trigger a notification. In case you need the opposite, it is very easy to invert the behavior of the code.

The example should output: Creating data1 without notification for attrs name & surname
Creating data2 without notification for attr age
Setting data1.name=Heather - Notification unnecessary
Setting data1.num=333 - Notification expected
Observer1: Subject Heather has updated attr num to 333
Setting data2.name=Molly - Notification expected
Observer2: Subject Molly has updated attr name to Molly
Setting data2.age=28 - Notification unnecessary
Setting data2.eyecolor=blue - Notification expected
Observer2: Subject Molly has updated attr eyecolor to blue

Observer Pattern (Python)

2013-02-04T20:55:10-08:00

Python recipe 578449 by Ilya Pashchenko (oop).

The example should output: Setting Data 1 = 10 DecimalViewer: Subject Data 1 has data 10 HexViewer: Subject Data 1 has data 0xa Setting Data 2 = 15 HexViewer: Subject Data 2 has data 0xf DecimalViewer: Subject Data 2 has data 15 Setting Data 1 = 3 DecimalViewer: Subject Data 1 has data 3 HexViewer: Subject Data 1 has data 0x3 Setting Data 2 = 5 HexViewer: Subject Data 2 has data 0x5 DecimalViewer: Subject Data 2 has data 5 Detach HexViewer from data1 and data2. Setting Data 1 = 10 DecimalViewer: Subject Data 1 has data 10 Setting Data 2 = 15 DecimalViewer: Subject Data 2 has data 15

Factory pattern (Python)

2013-02-04T21:12:27-08:00

Python recipe 578450 by Ilya Pashchenko (oop).

In the factory pattern you have an object that creates other objects.

Python: A event/signal dispatcher (Python)

2013-07-29T05:34:24-07:00

Python recipe 578307 by Esteban Castro Borsani (dispatcher, events, oop, python, signals).

This is a thread-safe dispatcher.

Bound Method Weakref (Python)

2013-07-29T05:35:55-07:00

Python recipe 578298 by Esteban Castro Borsani (oop, python, weakref). Revision 4.

This is a workaorund for weak reference bound methods. It may be useful for observer patterns.

Singleton? We don't need no stinkin' singleton: the Borg design pattern (Python)

2011-09-18T18:47:59-07:00

Python recipe 577870 by Anler Hernández Peral (oop, pattern).

The Singleton design pattern (DP) has a catchy name, but the wrong focus -- on identity rather than on state. The Borg design pattern has all instances share state instead, and Python makes it, literally, a snap.

Concrete Class Finder (Python)

2011-08-24T05:29:15-07:00

Python recipe 577858 by Lucio Santi (case, class, design, finder, match, oop, pattern, suitable, switch).

This recipe implements a design pattern useful for performing an object-oriented case analysis for a particular object (or a collection of objects as well). Essentially, it is an alternative to complex if-then-else or switches. Modelling each case with a particular class, the Concrete Class Finder searches for an appropriate case/class that applies to the given object/s. Once found, this class can be used in an homogeneous way, independently of the object/s previously considered.

Cache decorator in python 2.4 (Python)

2011-08-08T00:10:51-07:00

Python recipe 577827 by sivarama sarma (oop).

The latest version of Python introduced a new language feature, function and method decorators (PEP 318, http://www.python.org/peps/pep-0318.html). This recipe show a common callable transformation that can benefit from the new syntax, often referred to as Memoization pattern.

Infix operators (Python)

2011-06-06T12:07:00-07:00

Python recipe 577738 by Animesh Kumar (oop).

Python has the wonderful "in" operator and it would be nice to have additional infix operator like this. This recipe shows how (almost) arbitrary infix operators can be defined.

Item Properties (Python)

2012-05-09T23:24:55-07:00

Python recipe 577703 by Ian Kelly (decorator, descriptor, oop, property). Revision 2.

A property variation that allows property access using an index or key.

Infix operators (Python)

2005-02-17T11:12:04-08:00

Python recipe 384122 by Ferdinand Jamitzky (oop). Revision 3.

Python has the wonderful "in" operator and it would be nice to have additional infix operator like this. This recipe shows how (almost) arbitrary infix operators can be defined.

Attribute-based Framework 1: Basics (Python)

2010-07-21T21:40:54-07:00

Python recipe 577327 by Jack Trainor (educational, framework, oop, simulation). Revision 2.

I am adapting Prof. David Cheriton's OO software methodology to Python. It's an approach for building industrial-strength code with a disciplined architecture, consistent naming conventions, and a rigorous division of interface from implementation. I'll be adding more of his techniques in further recipes. These recipes are based on Cheriton's CS249a course at Stanford.

Attribute-based Framework 2: Notifications (Python)

2010-07-23T20:12:10-07:00

Python recipe 577330 by Jack Trainor (educational, framework, oop, simulation). Revision 2.

Default arg special action (Python)

2010-04-14T19:52:33-07:00

Python recipe 577194 by Ed Blake (default_arguments, identity, oop).

A way to allow functions with 0, 1, and -1 arguments! For those times you want to differentiate a no value argument from a non-value argument.

Calculations on huge (memmap-)arrays (Python)

2009-05-05T10:19:37-07:00

Python recipe 576739 by d.schlabing (memmap, numpy, oop). Revision 2.

This is a way of doing calculations on whole arrays that might be to big to fit into memory.

Curious Recursive Decorator Pattern (Python)

2009-05-16T10:00:22-07:00

Python recipe 576758 by Y S (decorator, oop). Revision 3.

There are no ABCs for ordering operations. This is because the recursive class difinition like:

 class Derived(XXX(Derived)):

is invalid syntax. This recipe implements an ABC ordering class with using decorator.

Easy State Pattern - support for implementing state machines (Python)

2009-06-15T11:25:17-07:00

Python recipe 576613 by Rodney Drenth (algorithms, decorators, metaclasses, oop, state_machine, state_pattern). Revision 3.

Provides is a module that gives support for implementing state machines. States are implemented as subclasses, derived from the state machine class. Methods that are state dependant or which cause transitions are declared using decorators. Because states can be subclasses of other states, common behaviour among several states is easily supported. The implementation allows for implementing multiple states or substates within a class.

This module best support statem achines implemeting controllers for embedded systems, implementing user interfaces, or in discrete event model simulation. Parsers, which generally have many states and where you would need to define a Transaction method for each different character encountered would be more easily implemented by other means.