Python中的多态性

什么是多态性：多态性这个词意味着具有多种形式。在编程中，多态意味着相同的函数名（但不同的签名）被用于不同的类型。
内置多态函数示例：

Python3

# Python program to demonstrate in-built poly-
# morphic functions
 
# len() being used for a string
print(len("geeks"))
 
# len() being used for a list
print(len([10, 20, 30]))

输出：

5
3

用户定义的多态函数示例：

Python3

# A simple Python function to demonstrate
# Polymorphism
 
def add(x, y, z = 0):
    return x + y+z
 
# Driver code
print(add(2, 3))
print(add(2, 3, 4))

输出：

5
9

类方法的多态性：
下面的代码展示了Python如何以相同的方式使用两种不同的类类型。我们创建了一个遍历对象元组的 for 循环。然后调用方法而不用关心每个对象是哪个类类型。我们假设这些方法实际上存在于每个类中。

Python3

class India():
    def capital(self):
        print("New Delhi is the capital of India.")
 
    def language(self):
        print("Hindi is the most widely spoken language of India.")
 
    def type(self):
        print("India is a developing country.")
 
class USA():
    def capital(self):
        print("Washington, D.C. is the capital of USA.")
 
    def language(self):
        print("English is the primary language of USA.")
 
    def type(self):
        print("USA is a developed country.")
 
obj_ind = India()
obj_usa = USA()
for country in (obj_ind, obj_usa):
    country.capital()
    country.language()
    country.type()

输出：

New Delhi is the capital of India.
Hindi is the most widely spoken language of India.
India is a developing country.
Washington, D.C. is the capital of USA.
English is the primary language of USA.
USA is a developed country.

具有继承的多态性：
在Python中，多态允许我们在子类中定义与父类中的方法同名的方法。在继承中，子类继承父类的方法。但是，可以修改从父类继承的子类中的方法。这在从父类继承的方法不太适合子类的情况下特别有用。在这种情况下，我们在子类中重新实现该方法。这种在子类中重新实现方法的过程称为Method Overriding 。

Python3

class Bird:
  def intro(self):
    print("There are many types of birds.")
     
  def flight(self):
    print("Most of the birds can fly but some cannot.")
   
class sparrow(Bird):
  def flight(self):
    print("Sparrows can fly.")
     
class ostrich(Bird):
  def flight(self):
    print("Ostriches cannot fly.")
     
obj_bird = Bird()
obj_spr = sparrow()
obj_ost = ostrich()
 
obj_bird.intro()
obj_bird.flight()
 
obj_spr.intro()
obj_spr.flight()
 
obj_ost.intro()
obj_ost.flight()

输出：

There are many types of birds.
Most of the birds can fly but some cannot.
There are many types of birds.
Sparrows can fly.
There are many types of birds.
Ostriches cannot fly.

具有函数和对象的多态性：
也可以创建一个可以接受任何对象的函数，允许多态性。在这个例子中，让我们创建一个名为“func()”的函数，它将接受一个我们将命名为“obj”的对象。虽然我们使用名称“obj”，但任何实例化的对象都可以被调用到这个函数中。接下来，让我们让函数使用我们传递给它的“obj”对象来做一些事情。在这种情况下，让我们调用三个方法，即capital()、language() 和type()，每个方法都在'India' 和'USA' 两个类中定义。接下来，让我们创建 'India' 和 'USA' 类的实例化，如果我们还没有的话。有了这些，我们可以使用相同的 func()函数调用它们的动作：

Python3

def func(obj):
    obj.capital()
    obj.language()
    obj.type()
  
obj_ind = India()
obj_usa = USA()
  
func(obj_ind)
func(obj_usa)

代码：用函数实现多态

Python3

class India():
    def capital(self):
        print("New Delhi is the capital of India.")
  
    def language(self):
        print("Hindi is the most widely spoken language of India.")
  
    def type(self):
        print("India is a developing country.")
  
class USA():
    def capital(self):
        print("Washington, D.C. is the capital of USA.")
  
    def language(self):
        print("English is the primary language of USA.")
  
    def type(self):
        print("USA is a developed country.")
 
def func(obj):
    obj.capital()
    obj.language()
    obj.type()
  
obj_ind = India()
obj_usa = USA()
  
func(obj_ind)
func(obj_usa)

输出：

New Delhi is the capital of India.
Hindi is the most widely spoken language of India.
India is a developing country.
Washington, D.C. is the capital of USA.
English is the primary language of USA.
USA is a developed country.