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Other implementations are possible: for example, objects in Python use associative key-value containers. [4] Some programming languages such as Eiffel support specification of invariants as part of the definition of the class, and enforce them through the type system.
Python supports most object oriented programming (OOP) techniques. It allows polymorphism, not only within a class hierarchy but also by duck typing. Any object can be used for any type, and it will work so long as it has the proper methods and attributes. And everything in Python is an object, including classes, functions, numbers and modules.
Python allows programmers to define their own types using classes, most often used for object-oriented programming. New instances of classes are constructed by calling the class (for example, SpamClass or EggsClass ()), and the classes are instances of the metaclass type (itself an instance of itself), allowing metaprogramming and reflection.
According to Design Patterns: Elements of Reusable Object-Oriented Software: "Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory method lets a class defer instantiation to subclasses." [2] Creating an object often requires complex processes not appropriate to include within a composing object.
A class diagram exemplifying the singleton pattern.. In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance.
Duck typing is similar to, but distinct from, structural typing.Structural typing is a static typing system that determines type compatibility and equivalence by a type's structure, whereas duck typing is dynamic and determines type compatibility by only that part of a type's structure that is accessed during runtime.
/*Ruby has three member variable types: class, class instance, and instance. */ class Dog # The class variable is defined within the class body with two at-signs # and describes data about all Dogs *and* their derived Dog breeds (if any) @@sniffs = true end mutt = Dog. new mutt. class. sniffs #=> true class Poodle < Dog # The "class instance variable" is defined within the class body with a ...
The Decorator Pattern (or an implementation of this design pattern in Python - as the above example) should not be confused with Python Decorators, a language feature of Python. They are different things. Second to the Python Wiki: The Decorator Pattern is a pattern described in the Design Patterns Book.