Python中的生成器

# 列表生成式
list_1 = [x**2 for x in range(10)]  # x**2处也可以放函数
print(list_1)   #[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# 代码等价于
list_2 = []
for x in range(10):
    list_2.append(x**2)
print(list_2)

list_1 = (x*2 for x in range(10) )

import time
start_time = time.time()
list_1 = (x*2 for x in range(10) )
stop_time = time.time()
print(list_1)
print("the list_1 run time is %s" % (stop_time-start_time))

start_time = time.time()
list_2 = [x*2 for x in range(10) ]
stop_time = time.time()
print(list_2)
print("the list_2 run time is %s" % (stop_time-start_time))

<generator object <genexpr> at 0x0000011FACD1ED60> 生成器只有一个列表地址，并没有具体的数值
the list_1 run time is 0.0
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
the list_2 run time is 0.0

>>>list_1 = (x*2 for x in range(100000000))
>>>for x in list_1:
          print(x)
>>>list_1.__next__
>>>list_1.__next__
>>>list_1.__next__

def fib(sum):
    a, b, c = 0, 1, 0
    while c < sum:
        print(b)
        a, b = b, a + b
        c += 1
fib(6)

def fib(sum):
    a, b, c = 0, 1, 0
    while c < sum:
        #print(b)
        yield b        # 代码执行到这里，会跳出这个函数，并将b的值返回到使用next的代码处
        a, b = b, a + b
        c += 1
# print(fib(6))  # 这里得到的就是生成器
p = fib(6)
print(next(p))
print(next(p))
print("做点别的事情")
print(next(p))
print(p.__next__())
print(next(p))
print(p.__next__())

>>> f = fib(6)
>>> f
<generator object fib at 0x104feaaa0

for n in fib(6):
     print(n)

def fib(sum):
    a, b, c = 0, 1, 0
    while c < sum:
        yield b
        a, b = b, a + b
        c += 1
    return "返回值只能传递给异常"

g = fib(3)
while True:
    try:
        x = next(g)
        print('g:', x)
    except StopIteration as e:
         print('Generator return value:', e.value)
         break
"""

g: 1
g: 1
g: 2
Generator return value: 返回值只能传递给异常
"""

#_*_coding:utf-8_*_
#通过生成器实现协程并行运算
import time
def consumer(name):
    print("%s 准备吃包子啦!" %name)
    while True:
       baozi = yield
       print("包子[%s]来了,被[%s]吃了!" %(baozi,name))

def producer(name):
    c = consumer(name)
    c2 = consumer('B')
    c.__next__()
    c2.__next__()
    print("老子开始准备做包子啦!")
    for i in range(10):
        time.sleep(1)
        print("做了2个包子!")
        c.send(i)　
        c2.send(i)

producer("飞某人")