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S R Q

Attributes

p265 You can assign values to an instance using dot. 
 
# Class attributes ...
#
# Use dot to assign values to a class instance

class Point:
    """ a 2D point """

p = Point()
p.x = 1
p.y = 2

assert p.x == 1
assert p.y == 2

Argument

You can pass an instance as an argument. 
 
# Function arguments ...
#
# Class instances can be pass as arguments to functions

class Point:
    """ a 2D point """

p = Point()
p.x = 1
p.y = 2

def print_point(point):
    print('(%s, %s)' % (point.x, point.y))

print_point(p) # (1, 2)

Docstring

The docstring lists the attributes. 
 
# Class definition ...
#
# Use docstring to lists attributes

 
class Rectangle:
    """Represents a rectangle.
    attributes: width, height, corner
    """

class Point:
    """A 2-D point"""
    # simple comment (not used by __doc__)

print(Rectangle.__doc__) 
    # Represents a rectangle.
    #     attributes: width, height, corner - Look Here

print(Point.__doc__) 
    # A 2-D point


box = Rectangle()
box.width = 100
box.height = 200
box.corner = Point() # corner - embeded object
box.corner.x = 10
box.corner.y = 20

assert box.width == 100
assert box.corner.x == 10

Distance

Distance between two points using a class Point(). 
 
# Function distance() ...
#
# Distance between two points ...
# takes 2 Point() objects as argument
# returns the distance between them

import math

class Point: """ a 2D point """

def distance_between_points(p1, p2):
    dx = (p2.x - p1.x)**2
    dy = (p2.y - p1.y)**2
    return math.sqrt(dx + dy)

a = Point()
a.x = 0
a.y = 0

b = Point()
b.x = 3
b.y = 4

assert distance_between_points(a, b) == 5

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Class, Functional