弱类型?强类型?动态语言,静态语言

弱类型: 在程序运行过程中,类型可变

动态

variables must necessarily be defined before they are used. But the good thing is that these variables need not be declared, and they need not be bound to a particular type. Python is a very good example of a dynamic typed programming language.

- 弱类型：> "1"+2'12'强类型：>>> "1"+2Traceback (most recent call last):  File "
    
     ", line 1, in 
     
      TypeError: cannot concatenate 'str' and 'int' objects动态类型:>>> a = 1>>> type(a)
      
       >>> a = "s">>> type(a)
       
        静态类型：Prelude> let a = "123" :: Int
        
         :2:9:    Couldn't match expected type `Int' with actual type `[Char]'    In the expression: "123" :: Int    In an equation for `a': a = "123" :: Int
        
       
      
     
    

鸭子类型的典故

只要拥有动物的talk方法,就可以去使用meeting方法. 而不必一定要是anaimal的子类, 总得找个合适的比喻来描述吧. 像是鸭子,会叫,就把他当成鸭子, 像是狗会狗叫,就当他是狗, 只不过我们一般用鸭子来比喻.

“A bird that walks like a duck and swims like a duck and quacks like a duck, is a duck.”

The actual Apparel of an entity doesn't matter if the entity does all the intended things.

In other words, don't check whether it IS-A duck,check whether it QUACKS-like-a duck, WALKS-like-a duck, etc. depending on exactly what subset of duck-like behavior you need for your program.

class Duck:    def quack(self):         print "這鴨子在呱呱叫"    def feathers(self):         print "這鴨子擁有白色與灰色羽毛" class Person:    def quack(self):        print "這人正在模仿鴨子"    def feathers(self):         print "這人在地上拿起1根羽毛然後給其他人看" def in_the_forest(duck):    duck.quack()    duck.feathers() def game():    donald = Duck()    john = Person()    in_the_forest(donald)    in_the_forest(john)game()