python继承和抽象类的实现方法

本文实例讲述了python继承和抽象类的实现方法。分享给大家供大家参考。

具体实现方法如下：

#!/usr/local/bin/python

# 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 earnings(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 class, 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 CommissionWorker's pay"""

 

      return self.salary + self.commission * self.quantity

 

   def __str__(self):

      """String representation of CommissionWorker"""

 

      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, inherits 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())

输出结果如下：

Boss: John Smith earned $800.00

Commission Worker: Sue Jones earned $650.00

Piece Worker: Bob Lewis earned $500.00

Hourly Worker: Karen Price earned $550.00

希望本文所述对大家的Python程序设计有所帮助。