python 生成器&迭代器

s = (x*2 for x in range(5))

# 生成器的调用方法：next()
print(next(s))   # 提取生成器里面的值，in python2中等价于 s._next_()，next() 一次打印一次

print(next(s))
print(next(s))

# 生成器就是一个可迭代对象(Iterable)
for i in s:         # 遍历生成器可迭代对象
    print(i)         # 打印完一个数之后这个数就被回收，不占用内存，只占用被引用值的哪一个内存

def fun():         # 注意：生成器对象是fun()，而不是fun
    print('s')
    yield 1

    print('ss')
    yield 2

g = fun()
print(g)           # <generator object fun at 0x000001D54E12A0F8>
 
next(g)            # 有返回值，为yield后的值
next(g)

def fun():   
    print('s')
    yield 1

    print('ss')
    yield 2

for i in fun():
    print(i)       # yield 有返回值，返回值赋给了i

def fib(maxs):
    n, before, after = 0, 0, 1
    while n < maxs:
        print(after)       # 从1开始，如打印before则从从0开始
        before, after = after, before+after      # 先计算后赋值（先右后左）
        n = n+1

fib(10)     # 输出前10个斐波那契数

before = after
after =  before+after

def fib(maxs):
    n, before, after = 0, 0, 1
    while n < maxs:
        yield before
        before, after = after, before+after      # 先计算后赋值（先右后左）
        n = n+1

g = fib(8)
print(g)     # 生成器所在的内存地址

# 需要几个next() 几次，但最多不能超过8次，否则应修改fib() 里面的数字
print(next(g))
print(next(g))
print(next(g))
print(next(g))

def fun():        # fun()是一个生成器对象而不是fun
    print('qwer')
    count = yield 1  # 先把yield的值返回，然后把‘xss’赋值给变量count
    print(count)

    print('asdf')
    yield 2

f = fun()
# next(f)      # 进入函数体
f.send(None)   # 等价于next(f)  

s = f.send('xss')   # 给yield前面的变量赋值
print(s)    

import time

def consumer(name):
    print("%s准备吃包子！" % name)
    while True:
        baozi = yield
        print("包子[%s]来了，被[%s]吃了！" % (baozi, name))

def producer(name):
    a1 = consumer('A')
    a2 = consumer('B')
    next(a1)
    next(a2)
    print("%s准备吃包子了！" % name)
    for i in range(5):
        time.sleep(1)
        print("做了2个包子")
        a1.send(i)
        a2.send(i)

producer("xiaoss")

while:
    try:
        I = next(list_Iterator)
    
    except StopIteration:
        break

from collections import Iterable,Iterator   # 调用Iterable和Iterator

lis = [1, 2, 3, 4]
d = iter(lis)   # 相当于 l._iter_()
print(d)        # <list_iterator object at 0x00000206700DC358>
print(next(d))
print(next(d))
print(next(d))
print(next(d))

for i in [1, 2, 3, 4]:
    iter([1, 2, 3, 4])

print(isinstance([1, 2], list))    # 判断一个字符是不是某个特定的数据类型 isinstance(数据, 数据类型)
print(isinstance(lis, Iterable))   # 判断lis是不是迭代器

F = max(len(x.strip()) for x in open('file_1', 'r'))      # 文件读取，找出最长的行
print(F)       # 最长行字符的个数