Lesson 16 Notes: Classes and Methods

• So, what's a class?
  • Remember functions?
  • Functions are collections of commands that can be used over and over again.
  • Classes are similar
  • Classes are collections of data and functions that can be used over and over.
• How to Create a Class:
  class MyClass:
    def hello(self):
        print "Welcome."
    def math(self, v1, v2):
        print v1+v2
  • Start with keyword "class"
  • Class names are capitalized by convention
  • End line with colon, then create body of class
  • In body, create function definitions.
  • Each function must take "self" as a parameter.
• Using a Class
  class MyClass:
    def hello(self):
        print "Welcome."
    def math(self, v1, v2):
        print v1+v2
fred = MyClass()
fred.hello()
fred.math(2,4)
  • Create an instance of a class by assigning a variable name to it.
  • To apply a function to the new instance, you must use a fully qualified name --instance.method()
  • If the method takes an argument, be sure to include all needed values.
• A Gradebook Sample Class
  class Gradebook:
   def __init__(self, name, value):
        self.name = name
        self.grade = value
        self.scores = 1
    def addgrade(self, points):
        self.scores += 1
        self.grade += points
        self.average = int(float(self.grade)/self.scores)
        print self.name, ": average =", self.average
  • Variables inside a class must be accessed by prefixing the variable name with "self."
  • The __init__ function is is run whenever a new instance of the class is created.
• Using The Gradebook Class
  eli = Gradebook('Eli', 85)
benji = Gradebook('Benji', 90)
beryl = Gradebook('Beryl', 61)

eli.addgrade(92)
benji.addgrade(91)
beryl.addgrade(13)

eli.addgrade(88)
benji.addgrade(89)
beryl.addgrade(92)
  • Each new instance of the Gradebook class must have name and first score, because that is what our __init__ function requires.
  • Each new instance of the Gradebook class must have name and first score, because that is what our __init__ function requires.
  • Each instance will have its own separate average.
• Review
  • What is a class?
  • What is an instance?
  • How do you create and instance of a class?
  • How do you use a method within a class?
  • What is the __init__ function?