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Constructors often have the same name as the declaring class. They have the task of initializing the object's data members and of establishing the invariant of the class, failing if the invariant is invalid. A properly written constructor leaves the resulting object in a valid state. Immutable objects must be initialized in a constructor.
The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type.
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.
Since relational databases do not store objects directly (though some RDBMSs have object-oriented features to approximate this), there is a general need to bridge the two worlds. The problem of bridging object-oriented programming accesses and data patterns with relational databases is known as object-relational impedance mismatch .
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.
Even though object-oriented seems like a superset of object-based, they are used as mutually exclusive alternatives, rather than overlapping. [citation needed] Examples of strictly object-based languages – supporting an object feature but not inheritance or subtyping – are early versions of Ada, [2] Visual Basic 6 (VB6), and Fortran 90.
A language that supports object creation via a template object is classified as prototype-based. The concept of object is used in many different software contexts, including: Possibly the most common use is in-memory objects in a computer program written in an object-based language. Information systems can be modeled with objects representing ...
The object methods include access to the object state (via an implicit or explicit parameter that references the object) whereas class methods do not. If the language supports inheritance , a class can be defined based on another class with all of its state and behavior plus additional state and behavior that further specializes the class.