yield实例

时间:2022-03-18 16:26:49

如下

# __author__ = liukun
# coding:utf-8
def it():
print ('hello')
yield 1
yield 1
a= it()
print("#############")
print(a)
print("*************")
for i in a:
print (i)

结果:

/Library/Frameworks/Python.framework/Versions/3.5/bin/python3.5 /Applications/PyCharm.app/Contents/helpers/pycharm/utrunner.py /Users/kamil/PycharmProjects/untitled4/Day5/python基础教程/test.py true
Testing started at 下午4:33 ...
#############
<generator object it at 0x1016babf8>
*************
hello
1
1 Process finished with exit code 0
Empty test suite.

从上面可以看出当执行generator函数的时候仅仅做的是生成了一个特殊的iterator对象,并没有执行里面的内容

再来

a = 1
def it():
global a
yield 3
a += 1
yield 4
for i in it():
print ("i=%d;a=%d" %(i,a)) '''

i=3;a=1
i=4;a=2

'''

如果:

a = 1
def it():
global a
a += 1
yield 3
yield 4
for i in it():
print ("i=%d;a=%d" %(i,a))
'''

i=3;a=2
i=4;a=2

'''

yield的作用就是,每次发生next()调用,函数执行完yield语句之后在挂起,这时返回yield的值(你愿意yield啥就yield啥),整个函数状态被保存,等待下一次next()调用;下次next()调用发生时,从yield后的语句开始执行(有yiled也在循环体内,未必一定是顺序的),直到再次遇到yield为止,然后重复删除动作