Objectives
- Create a class
- Create functions/methods within a class
- Create an object from a class
- Implement a constructor
- Implement a destructor
Class overview
- a class is created using the keyword: class
- functions that are part of objects are usually called methods
- class methods must have a first parameter: self
- the self parameter is supplied automatically by Python when calling
- a constructor is a method run at object instantiation to initialize the object
- the constructor method for Python objects is called: __init__
Class and constructor example
class Employee: count = 0 # could make private using: __count def __init__(self, id="** No ID **", name=""): """Constructor""" self.id = id self.name = name Employee.count += 1 def die(self): """Destructor""" Employee.count -= 1 def talk(self): if (len(self.name) > 0): print('{} says, "Hello!"'.format(self.name)) else: print("Hi.") def __str__(self): if len(self.name) == 0: return "{0} ({1})".format("Unknown", self.id) else: return "{0} ({1})".format(self.name, self.id) @classmethod def getCount(cls): """Returns object count""" return cls.count emp = Employee() emp.talk() barney = Employee(name="Barnaby", id="715563") barney.talk() print("There are {0} employees".format(Employee.getCount())) print(emp) print(barney) emp.die() barney.die() print("Both employees let go. Now there are {0}.".format(Employee.getCount()))