python编程金典的一些例子

#Fig 9.9:fig09_09.py #creating a class hierarchy with an abstract base class. class Employee: """Abstract base class Employee""" def __init__(self,first,last): """Employee constructor,takes first name and last name. Note:Cannot create object of class Employee.""" if self.__class__==Employee: raise NotImplementedError,\ "Cannot create object of class Employee" self.firstName=first self.lastName=last def __str__(self): """String representation of Employee""" return "%s %s"%(self.firstName,self.lastName) def _checkPositive(self,value): """Utility method to ensure a value is positive""" if value<0: raise ValueError,\ "Attribute value (%s) must be positive"%value else: return value def earnnings(self): """Abstract method:derived classes must override""" raise NotImplementedError,"Cannot call abstract method" class Boss(Employee): """Boss class,inherits from Employee""" def __init__(self,first,last,salary): """Boss constructor,takes first and last names and salary""" Employee.__init__(self,first,last) self.weeklySalary=self._checkPositive(float(salary)) def earnings(self): """Compute the boss's pay""" return self.weeklySalary def __str__(self): """String representation of Boss""" return "%17s:%s"%("Boss",Employee.__str__(self)) class CommissionWorker(Employee): """CommissionWorker c;lass, inherits from Employee""" def __init__(self,first,last,salary,commission,quantity): """CommissionWorker constructor,takes first and last names, salary,commission and quantity""" Employee.__init__(self,first,last) self.salary=self._checkPositive(float(salary)) self.commission=self._checkPositive(float(commission)) self.quantity=self._checkPositive(quantity) def earnings(self): """Compute the CommisionWorker's pay""" return self.salary+self.commission*self.quantity def __str__(self): """Strings representation of CommisionWorker""" return "%17s:%s"%("Commission Worker", Employee.__str__(self)) class PieceWorker(Employee): """PieceWorker class,inherits from Employee""" def __init__(self,first,last,wage,quantity): """PieceWorker constructor, takes first and last names, wage per piece and quantity""" Employee.__init__(self,first,last) self.wagePerPiece=self._checkPositive(float(wage)) self.quantity=self._checkPositive(quantity) def earnings(self): """Compute PieceWorker's pay""" return self.quantity*self.wagePerPiece def __str__(self): """String representation of PieceWorker""" return "%17s:%s"%("Piece Worker",Employee.__str__(self)) class HourlyWorker(Employee): """HourlyWorker class, inhertits from Employee""" def __init__(self,first,last,wage,hours): """HourlyWorker constructor,takes first and last names, wage per hour and hours worked""" Employee.__init__(self,first,last) self.wage=self._checkPositive(float(wage)) self.hours=self._checkPositive(float(hours)) def earnings(self): """Compute HourlyWorker's pay""" if self.hours<=40: return self.wage*self.hours else: return 40*self.wage+(self.hours-40)*\ self.wage*1.5 def __str__(self): """String representation of HourlyWorker""" return "%17s:%s"%("Hourly Worker", Employee.__str__(self)) #main program #create list of Employees employees=[Boss("John","Smith",800.00), CommissionWorker("Sue","Jones",200.0,3.0,150), PieceWorker("Bob","Lewis",2.5,200), HourlyWorker("Karen","Price",13.75,40)] #print Employee and compute earnings for employee in employees: print"%s earned $%.2f"%(employee,employee.earnings())