Classes
=======

Object-oriented programming (OOP)
---------------------------------

Object-oriented programming is a method of programing that bundles behaviors and properties into objects.  OOP is supported by Python.   A class is a blueprint for an object.  In this section we will show how to define a class, give the class attributes and methods, and use class inheritance.

A class has a form like this:

..code::

 class ClassName:
   # Class attribute
   (statement)
  
   # instance attributes
   def __init__(self, name, age):
       self.attr1 = value
   .
   .
   .
   # instance methods
   def method1(self, para1):
       body
   .
   .
   .

**A Class with Attributes and Methods**

For our example we will create object that represent a person.   Each of these objects wiil have two attributes and two methods.

It is standard practice to use a capital letter for `naming a class <https://www.python.org/dev/peps/pep-0008/#class-names>`_.

We define our properties and set the initial state by defining the .__init__( )

.. code::

 class Person:
     # Class attribute
     species = 'human'
  
     def __str__(self):
         return f"{self.name} is a {self}."
     
     # instance attributes
     def __init__(self, name, age):
         self.name = name
         self.age = age
        
     # instance methods
     def greets(self, phrase):
         return f'{self.name} says, {phrase}.'
	
     def responds(self, phrase):
         return f'{self.name}, replies {phrase}.'

**Class Inheritance**

.. code::

 class Female(Person):
     gender = 'female'
     likes = 'movies'
  
     def responds(self, phrase='get lost'):
     return super().responds(phrase)
  
 class Male(Person):
     gender = 'male'
     likes = 'sports'

     def greets(self, phrase='what\'s your sign'):
         return super().greets(phrase)

Class Customization
-------------------

A class in Python can implement certain operations by defining methods with `special method names <https://docs.python.org/3/reference/datamodel.html#special-method-names>`_. 

* __repr__
* __str__
* define an ordering by defining __gt__ and __ge__  



`__repr__ <https://docs.python.org/3/reference/datamodel.html#object.__repr__>`_:  Called by the repr() built-in function to compute the “official” string representation of an object.
`__str__ <https://docs.python.org/3/reference/datamodel.html#object.__str__>`_:   Called by str(object) and the built-in functions format() and print() to compute the “informal” 
or nicely printable string representation of an object.

.. code::

 class Order:
     description = 'Ordering'

     def __init__(self, position):
         self.position = position
    
     def __gt__(self, other):
         value = self.position < other.position
         return value
    
     def __ge__(self, other):
         value = self.position <= other.position
         return value
    
     def __repr__(self):
         return f'<Order({self.position})>'
    
     def __str__(self):
         return f'\"Order({self.position})\"'