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Object Oriented Programming

Objects contain both data and functionality together
vs. Procedural Programming which is simply a list of statements
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Class

A Class defines a new data type

Built in data types are:
int
float
string
list

Lets build a data type for a point
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A point is two numbers (x,y) that is treated as a single object

Before we created a list with two numbers 
p = [x,y]
And we accessed it with 
p[0] and p[1]

A class lets us define a new type with attributes (data) and methods (functions) 
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class Point:
	# This represents a 2d point (x,y)
	def __init__(self,,y):
		self.x = x
		self.y = y
		
Creating a new instance of the object time is called instantiating
>>> myPoint = Point(1,2)
init is a method that is invoked when an object is instantiated
the first parameter of this method should be self, followed by the parameters to set up the attributes of Point
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We can set defaults with the init method
class Point:
	# This represents a 2d point (x,y)
	def __init__(self,x=0,y=0):
		self.x = x
		self.y = y
		
If Point() is instantiated without parameters, the instance will set its attributes to the default (0,0)
>>> p1 = Point()
# p1 now has (0,0)
>>> p1 = Point(1,2)
# p1 now has (1,2)
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__str__ method returns the string representation of the object
class Point:
	# This represents a 2d point (x,y)
	def __init__(self,x=0,y=0):
		self.x = x
		self.y = y
	
	def __str__(self):
		return "(" + str(self.x) + ", " + str(self.y) + ")"
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Besides __init__ and __str__ we can create any methods we like
class Point:
	# This represents a 2d point (x,y)
	def __init__(self,x=0,y=0):
		self.x = x
		self.y = y
		
	def __str__(self):
		return "(" + str(self.x) + ", " + str(self.y) + ")"
	
	def moveUpAndRight(self):
		self.x += 1
		self.y += 1
		
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Operator Overloading

We can change the way built in operators work for our classes
What happens if we try

p = Point(1,2)
q = Point(2,2)
r = p + q

>>> r = p + q
TypeError: unsupported operand type(s) for +: 'Point' and 'Point'
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We need to overload the + operator to know how to add points
using __add__

class Point:
	# This represents a 2d point (x,y)
	def __init__(self,x=0,y=0):
		self.x = x
		self.y = y
		
	def __str__(self):
		return "(" + str(self.x) + ", " + str(self.y) + ")"
		
	def __add__(self,otherPoint):
		return Point(self.x + otherPoint.x, self.y + otherPoint.y)
	
	def moveUpAndRight(self):
		self.x += 1
		self.y += 1
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Exercise
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