Python - Class and Objects

Posted 2020-08-01

Object-oriented programming

Python is OOP, Usually, each object definition corresponds to some object or concept in the real world and the functions that operate on that object correspond to the ways real-world objects interact. 

In python, every value is actually an object. An object has a state and a collection of methods that it can perform.

The state of an object represents those things that the object knows about itself. 

 

User Defined Classes

 

1  class Point:
3     """ Point class for representing and manipulating x,y coordinates. """
4 
5     def __init__(self):
6         """ Create a new point at the origin """
7         self.x = 0
8         self.y = 0

 

Every class should have a method with the special name _init_. This is Initializer method often called constructor.

A method behaves like a function but it is invoked on a specific instance.

The _str_ method is responsible for returning a string representation as defined by the class creator. 

 

class Point:
    """ Point class for representing and manipulating x,y coordinates. """

    def __init__(self, initX, initY):
        """ Create a new point at the origin """
        self.x = initX
        self.y = initY

　　def _str_(self):
　　　　return "x=" + str(self.x) + ", y=" + str(self.y)
　　
　　def getX(self):
　　　　return self.x

　　def getY(self):
　　　　return self.y

　　def distanceFromOrigin(self):
　　　　return ((self.x ** 2) + (self.y ** 2)) ** 0.5

　　def halfway(self, target):
　　　　mx = (self.x + target.x) / 2
　　　　my = (self.y + target.y) / 2
　　　　return Point(mx, my)

def distance(point1, point2):
　　xdiff = point2.getX() - point1.getX()
　　ydiff = point2.getY() - point1.getY()

　　dist = math.sqrt(xdiff ** 2 + ydiff ** 2)
　　return dist

p = Point(7,6)         # Instantiate an object of type Point
q = Point(2,2)         # and make a second point
mid = p.halfway(q)

print(mid)
print(mid.getX())
print(mid.getY())
print(p)
print(p.getX())
print(p.getY())
print(p.distanceFromOrigin())
print(q)
print(distance(p,q))
print(p is q)