yield
其实yield 是针对generator 的一种，通过yield 可以输出以及去除元素，
类似列表的remove和for 循环结合使用，下面是两个例子
def simpleGen():
yield 1
yield '2 --> punch!'
yield '3 --> punch!1'
myG = simpleGen()
print(next(myG))
print(next(myG))
print(myG)
for i in myG:
print(i)
下面这个例子很好的解释了yield的作用，并且yield占用空间内存小
from random import randint
def randGen(aList):
while len(aList) > 0:
print(len(aList))
yield aList.pop(randint(-1, len(aList)-1))
aList=[1,2,3,4,5,5,6,78,8,9,9,9,9]
# randGen(aList) #yield 会把函数变为一个generator，所以直接这样不返回任何数据
a=randGen(aList)
print(next(a))
print(next(a))
print(next(a))
print(next(a))
print(aList)
# 13
# 3
# 12
# 5
# 11
# 2
# 10
# 9
# [1, 4, 5, 6, 78, 8, 9, 9, 9]
yield 的正确用法
def counter(start_at=0):
count = start_at
while True:
val = (yield count)
if val is not None:
count = val
else:
count += 1
count = counter()
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
print(next(count))
