迭代和生成器

'''列表迭代的本质:__iter()__函数返回一个迭代器，然后可以调用迭代器上的next方法'''
arr = [1,2,3,4,5]
arr_iterator = arr.__iter__()
print(arr_iterator.__next__())
print(next(arr_iterator))

　　

'''一个典型的迭代器实现。例子来自《流畅的python》.'''
import re
import reprlib

RE_WORD = re.compile('w+')

class Sentence:
    def __init__(self,text):
        self.text = text
        self.words = RE_WORD.findall(text)

    def __repr__(self):
        return 'Sentence(%s)' %reprlib.repr(self.text)

    def __iter__(self):
        return SentenceIterator(self.words)

class SentenceIterator:
    def __init__(self,words):
        self.words = words
        self.index = 0

    def __next__(self):
        try:
            word = self.words[self.index]
        except IndexError:
            raise StopIteration()
        self.index += 1
        return word

    def __iter__(self):
        return self

s = Sentence('abDdd a dd dw')
for i in s:
    print(i)

　　

'''用生成器创建的迭代对象。'''
def frange(start, stop, increment):
    x = start
    while x < stop:
        yield x
        x += increment

for i in frange(0,5,0.5):
    print(i)

　　

'''用生成器实现费波切纳算法'''
import sys

def fibonacci(n):  # 生成器函数 - 斐波那契
    a, b, counter = 0, 1, 0
    while True:
        if (counter > n):
            return
        yield a
        a, b = b, a + b
        counter += 1

f = fibonacci(10)  # f 是一个迭代器，由生成器返回生成
while True:
    try:
        print(next(f), end=" ")
    except StopIteration:
        sys.exit()