生成器

# 什么是生成器？只要在函数内部出现yield的关键字，那么再执行函数时，就不会执行函数体代码，会得到一个结果，该结果就是生成器
# def func():
#     print('>>:1')
#     yield 1
#     print('>>:2')
#     yield 2
#     print('>>:3')
#     yield 3
#
# g=func()
# print(g) # <generator object func at 0x000001FE953A8DC8>
# g.__next__()
# g.__iter__()
# 生成器就是迭代器
# res1=next(g) # >>:1
# print(res1) # 1
# res2=next(g) # >>:2
# print(res2) # 2
# res3=next(g) # >>:3
# print(res3) # 3

# yield的功能：
# 为我们提供了一种自定义迭代器对象的方法
# yield与return的区别在于yield可以返回多次值，函数暂停与再继续的状态是由yield帮忙保存的

# obj=range(1,100000000000000000000000000000000000,9527)
# print(obj) # range(1, 100000000000000000000000000000000000, 9527)

# range得到的是一个可迭代对象
# obj_iter=obj.__iter__()
# print(next(obj_iter)) # 1
# print(next(obj_iter)) # 9528
# print(next(obj_iter)) # 19055

# def my_range(start,stop,step=1):
#     while start < stop:
#         yield start
#
# g=my_range(1,6,2)
# print(next(g)) # 1
# print(next(g)) # 1
# print(next(g)) # 1

# def my_range(start,stop,step=1):
#     while start < stop:
#         yield start
#         start += step
#
# g=my_range(1,6,2)
# print(next(g)) # 1
# print(next(g)) # 3
# print(next(g)) # 5]

# tail -f access.log/grep'404'
# import time
# def tail(filepath):
#     with open(filepath,'rb')as f:
#         f.seek(0,2)
#         while True:
#             line=f.readline()
#             if line:
#                 yield line
#             else:
#                 time.sleep(0.05)
#
# lines=tail('a.txt')
# # print(lines) # <generator object tail at 0x0000028E6A7A0448>
# def grep(lines,pattern):
#     for line in lines:
#         line=line.decode('utf-8')
#         if pattern in line:
#             print(line)
#
# grep(lines,'404')
#
# def grep(lines,pattern):
#     for line in lines:
#         line=line.decode('utf-8')
#         if pattern in line:
#             yield line
#
# g=grep(tail('a.txt'),'404')
# print(g)
#
# for line in lines:
#     print(line)

# 了解知识点：
# yield表达式形式的用法
# def eater(name):
#     print('%s start eat'%name)
#     while True:
#         food=yield
#         print('%s start eat %s'%(name,food))
#
# e=eater('Alice')
# # 首先初始化
# next(e) # Alice start eat
# # 然后e.send 1、从暂停的位置，将值传给yield;2、与next一样
# e.send('blueberry') # Alice start eat blueberry
# e.send('Mulberry') # Alice start eat Mulberry
# e.send('Apple') # Alice start eat Apple

# def eater(name):
#     print('%s start eat'%name)
#     food_list=[]
#     while True:
#         food=yield food_list
#         food_list.append(food)
#         print('%s start eat %s'%(name,food))
#
# e=eater('Alice')
# print(e.send(None))
# print(e.send('blueberry'))
# print(e.send('Mulberry'))
# print(e.send('Apple'))
'''
Alice start eat
[]
Alice start eat blueberry
['blueberry']
Alice start eat Mulberry
['blueberry', 'Mulberry']
Alice start eat Apple
['blueberry', 'Mulberry', 'Apple']
'''