Python从2.6版本后中将has_key换成in

previous = {0: 0 , 1: 1}
def fibonacci(n):
if previous.has_key(n):
   return previous [ n ]
else:

   new value = fibonacci(n-1) + fibonacci(n-2)
   previous [ n ] = new value
   return new value

 

这个方法是python 2.6以后支持的，但在python 3.0版本开始将使用in。上面的代码可以改为:

 

previous = {0: 0 , 1: 1}
def fibonacci(n):
if n in previous:
    return previous [ n ]
else:

    new value = fibonacci(n-1) + fibonacci(n-2)
    previous [ n ] = new value
    return new value