Python迭代器协议及for循环工作机制详解

l=[1,2,3,4,5]
#下标访问方式
print(l[0])
print(l[7]) #超出访问会报IndexError: list index out of range

#遵循迭代器协议的方式
diedai=l.__iter__()
print(diedai.__next__())
print(diedai.__next__())
print(diedai.__next__())
print(diedai.__next__())
print(diedai.__next__())
print(diedai.__next__()) #超出边界会报StopIteration

#for循环访问方式：
#for循环本质就是遵循迭代器协议的访问方式，先调用diedai.__iter__（）方法，或者直接diedai=iter(l),然后依次执行diedai.next(),直到for循环捕捉到StopIteration终止循环
#for循环所有对象的本质都是一样的道理

for i in l:     #diedai=l.__iter__()
  print(l[i])   #i=diedai.next()

#使用while模拟for循环做的事情
diedai_l=l.__iter__()
while True:
  try:
    print(diedai_l.__next__())
  except StopIteration:
    print("迭代完毕，终止循环")
    break

import time
# def producer():
#   ret=[]
#   for i in range(100):
#     time.sleep(0.1)
#     ret.append('包子%s' %i)
#   return ret
#
# def consumer(res):
#   for index,baozi in enumerate(res):
#     time.sleep(0.1)
#     print('第%s个人，吃了%s' %(index,baozi))
#
# res=producer()
# consumer(res)




#yield 3相当于return 控制的是函数的返回值
#x=yield的另外一个特性，接受send传过来的值,赋值给x
# def test():
#   print('开始啦')
#   firt=yield #return 1  first=None
#   print('第一次',firt)
#   yield 2
#   print('第二次')
#
# t=test()
# res=t.__next__() #next(t)
# print(res)
# # t.__next__()
# # res=t.send(None)
# res=t.send('函数停留在first那个位置，我就是给first赋值的')
# print(res)





# def producer():
#   ret=[]
#   for i in range(100):
#     time.sleep(0.1)
#     ret.append('包子%s' %i)
#   return ret

def consumer(name):
  print('我是[%s],我准备开始吃包子了' %name)
  while True:
    baozi=yield
    time.sleep(1)
    print('%s 很开心的把【%s】吃掉了' %(name,baozi))

def producer():
  c1=consumer('wupeiqi')
  c2=consumer('yuanhao_SB')
  c1.__next__()
  c2.__next__()
  for i in range(10):
    time.sleep(1)
    c1.send('包子 %s' %i)
    c2.send('包子 %s' %i)
producer()

#1、三元表达式
name="alex"
name="yangyl"
res="1" if name=="yangyl" else "2"
print(res)

egg_list=["鸡蛋%s" %i for i in range(10) ]  #列表解析
print(egg_list)

#使用生产器获取
egg_two=("鸡蛋%s" %i for i in range(10))   #生产器表达式
print(egg_two)
print(egg_two.__next__())
print(next(egg_two))      #next()本质就是调用__next__