What is the difference between class and namespace in c

Change Language. Related Articles. Table of Contents. Save Article. Improve Article. Like Article. WheelCollection wheels;. The TypeScript docs are an open source project. Was this page helpful? Validators in a single file ts. ZipCodeValidator ;. The other kind of instance attribute reference is a method. In Python, the term method is not unique to class instances: other object types can have methods as well.

For example, list objects have methods called append, insert, remove, sort, and so on. Valid method names of an instance object depend on its class. By definition, all attributes of a class that are function objects define corresponding methods of its instances. So in our example, x. But x. In the MyClass example, this will return the string 'hello world'.

However, it is not necessary to call a method right away: x. For example:. What exactly happens when a method is called? You may have noticed that x. What happened to the argument? Actually, you may have guessed the answer: the special thing about methods is that the instance object is passed as the first argument of the function.

In our example, the call x. If the name denotes a valid class attribute that is a function object, a method object is created by packing pointers to the instance object and the function object just found together in an abstract object: this is the method object.

When the method object is called with an argument list, a new argument list is constructed from the instance object and the argument list, and the function object is called with this new argument list. Generally speaking, instance variables are for data unique to each instance and class variables are for attributes and methods shared by all instances of the class:.

As discussed in A Word About Names and Objects , shared data can have possibly surprising effects with involving mutable objects such as lists and dictionaries. For example, the tricks list in the following code should not be used as a class variable because just a single list would be shared by all Dog instances:. If the same attribute name occurs in both an instance and in a class, then attribute lookup prioritizes the instance:.

In other words, classes are not usable to implement pure abstract data types. In fact, nothing in Python makes it possible to enforce data hiding — it is all based upon convention. On the other hand, the Python implementation, written in C, can completely hide implementation details and control access to an object if necessary; this can be used by extensions to Python written in C.

Clients should use data attributes with care — clients may mess up invariants maintained by the methods by stamping on their data attributes.

Note that clients may add data attributes of their own to an instance object without affecting the validity of the methods, as long as name conflicts are avoided — again, a naming convention can save a lot of headaches here. There is no shorthand for referencing data attributes or other methods! I find that this actually increases the readability of methods: there is no chance of confusing local variables and instance variables when glancing through a method.

Often, the first argument of a method is called self. This is nothing more than a convention: the name self has absolutely no special meaning to Python. Note, however, that by not following the convention your code may be less readable to other Python programmers, and it is also conceivable that a class browser program might be written that relies upon such a convention. Any function object that is a class attribute defines a method for instances of that class.

It is not necessary that the function definition is textually enclosed in the class definition: assigning a function object to a local variable in the class is also ok. Now f , g and h are all attributes of class C that refer to function objects, and consequently they are all methods of instances of C — h being exactly equivalent to g.

Note that this practice usually only serves to confuse the reader of a program. Methods may call other methods by using method attributes of the self argument:. Methods may reference global names in the same way as ordinary functions. The global scope associated with a method is the module containing its definition.

A class is never used as a global scope. While one rarely encounters a good reason for using global data in a method, there are many legitimate uses of the global scope: for one thing, functions and modules imported into the global scope can be used by methods, as well as functions and classes defined in it.

Each value is an object, and therefore has a class also called its type. It is stored as object. The syntax for a derived class definition looks like this:. The name BaseClassName must be defined in a scope containing the derived class definition. In place of a base class name, other arbitrary expressions are also allowed. This can be useful, for example, when the base class is defined in another module:.

Execution of a derived class definition proceeds the same as for a base class. When the class object is constructed, the base class is remembered. This is used for resolving attribute references: if a requested attribute is not found in the class, the search proceeds to look in the base class.

This rule is applied recursively if the base class itself is derived from some other class. Flow control. Function declaration. Lambda function declaration. Fundamental types. Function types. Compound types. Storage duration specifiers.

Default initialization. Value initialization. Zero initialization. Copy initialization. Direct initialization. Aggregate initialization. Constant initialization. Reference initialization. Value categories. Order of evaluation. Operator precedence. Alternative representations. Boolean - Integer - Floating-point.

Implicit conversions - Explicit conversions. Class declaration. Access specifiers. Virtual function. Default constructor.