In object-oriented programming class is a set (a transitive closure) of types bound by the relation of inheritance. It is said that all types derived from some base type T and the type T itself form a class T.

The first type T from the class T sometimes is called the root type of the class.

A class of types itself, as a type, has the values and operations of its own.
The operations of are usually called methods of the root type.
Both operations and values are called  polymorphic.

A polymorphic operation (method) selects an implementation depending on the actual specific type of the polymorphic argument.

The action of choice the type-specific implementation of a polymorphic operation is called dispatch. Correspondingly, polymorphic operations are often called dispatching or virtual.
Operations with multiple arguments and/or the results of the class are called multi-methods.
A further generalization of is the operation with arguments and/or results from different classes.

 single-dispatch languages are those that allow only one argument or result to control the dispatch. Usually it is the first parameter, often hidden, so that a prefix notation x.f() is used instead of mathematical f(x).
 multiple-dispatch languages allow many arguments and/or results to control the dispatch.


A polymorphic value has a type tag indicating its specific type from the class and the corresponding specific value of that type.
This type is sometimes called the most specific type of a [polymorphic] value.
The type tag of the value is used in order to resolve the dispatch.
The set of polymorphic values of a class is a transitive closure of the sets of values of all types from that class.

In many  OO languages
the type of the class of T and T itself are considered equivalent.
In some languages they are distinct (like in Ada).
When class T and T are equivalent, there is no way to distinguish
polymorphic and specific values.



Task

Create a basic class with a method, a constructor, an instance variable and how to instantiate it.




class MyClass:
    name2 = 2 # Class attribute
 
    def __init__(self):
        """
        Constructor  (Technically an initializer rather than a true "constructor")
        """
        self.name1 = 0 # Instance attribute
 
    def someMethod(self):
        """
        Method
        """
        self.name1 = 1
        MyClass.name2 = 3
 
 
myclass = MyClass() # class name, invoked as a function is the constructor syntax.
 
class MyOtherClass:
    count = 0  # Population of "MyOtherClass" objects
    def __init__(self, name, gender="Male", age=None):
        """
        One initializer required, others are optional (with different defaults)
        """
        MyOtherClass.count += 1
        self.name = name
        self.gender = gender
        if age is not None:
            self.age = age
    def __del__(self):
        MyOtherClass.count -= 1
 
person1 = MyOtherClass("John")
print person1.name, person1.gender  # "John Male"
print person1.age                   # Raises AttributeError exception!
person2 = MyOtherClass("Jane", "Female", 23)
print person2.name, person2.gender, person2.age  # "Jane Female 23"