生成器

生成器和迭代器

• 节省空间
• 惰性运算：边循环边处理
• 列表生成使用[]，生成器使用()

g = (i*i if i > 20 else i for i in a)

print(g)
print(next(g))
print(g.__next__())
print('-'*20)
for i in g:
    print(i)

• yield 保存了函数的中断状态

def fib(max):
    n,a,b = 0,0,1
    while n < max:
        yield b
        a,b = b,a+b
        n += 1
    return 'done'
    
f = fib(10)

print(f)
print(next(f))
print(next(f))
print('-'*20)
print(next(f))
print(next(f))
for i in f:
    print(i)

• send 将外部参数传到函数的yield中断里

吃包子游戏

import time
def consumer(name):
    print('%s 准备吃包子' % name)
    while 1:
        baozi = yield
        print('包子[%s]来了，被[%s]吃了' %(baozi,name))


def producer(name):
    c = consumer('Yaho')
    c2 = consumer('Ali')
    next(c)
    next(c2)

    print('开始做包子')
    for i in range(10):
        time.sleep(1)
        print('%s 做了2个包子出来' %name)
        c.send(i)
        c2.send(i)

producer('Steven')