Python Iterator for Fibonacci evaluation

The Fibonacci sequence (Fibonacci sequence), also known as the Golden Segment, is called the "Rabbit Sequence": F (0) =0,f (1) =1,f (n) =f (n-1) +f (n-2) (n≥2,n∈n*). For example 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233,377,610,987,1597,2584,4181,6765,10946,17711,28657,46368 ... This sequence starts with the 3rd item, each of which equals the sum of the first two items, and when n tends to infinity, the ratio of the previous item to the latter becomes more and more approximate to the golden ratio of 0.618.

　　python中可以被next()函数调用并不断返回下一个值的对象称为迭代器。用dir(list), dir(tuple) , dir(file) dir(dict) to see the properties of different types of objects, you will find that they all have a name of__iter__的特殊方法，对象有了这个属性，就能返回迭代器。迭代器不但可以作用于for循环，还可以被next()函数不断调用并返回下一个值，直到最后抛出StopIteration错误表示无法继续返回下一个值了。

The following is the implementation of Fibonacci evaluation using different methods

1. Simple version

# !/bin/env python def fib (n):     = 0, 1 for in      Range (n):        = B, a+    breturn  a Print ' f5 ',  fib (5)print'F10', fib (10)

Run results

F5 555

2. Recursive version

#!/bin/env pythondeffib (n):if0 = =N:return0elif1 = =N:return1Else:        returnFIB (n-1) + fib (n-2)Print 'f5', FIB (5)Print 'F10', FIB (10)

Run results

F5 555

3. Iterator version

classFib ():def __init__(self, N): SELF.A=0 self.b= 1SELF.N=N Self.count=0def __iter__(self):return SelfdefNext (self): res=self.a self.a, self.b= self.b, SELF.A +self.bifSelf.count >SELF.N:Raisestopiteration Self.count+ = 1returnResPrint 'f5', List (Fib (5))Print 'F10', List (Fib (10))

Run results

F5 [0, 1, 1, 2, 3, 51, 1, 2, 3, 5, 8, 13, 21, 34, 55]

There are many more things to do with iterators, such as reading files and so on.

Python Iterator for Fibonacci evaluation