13生成器函数

Posted 2020-09-21

一、生成器函数
#生成器函数：只要函数体包含yield关键字，该函数的执行结果就是生成器函数
#生成器就是迭代器

# def foo():
#     return 1
#     return 2
#     return 3
#     return 4
#
# res1=foo()
# print(res1)
#
# res2=foo()
# print(res2)





# def foo():
#     print(‘first‘)
#     yield 1
#     print(‘second‘)
#     yield 2
#     print(‘third‘)
#     yield 3
#     print(‘fourth‘)
#     yield 4
#     print(‘fifth‘)
#
# g=foo()
# for i in g:
#     print(i)



# print(g)
#
# print(next(g)) #触发迭代器g的执行，进而触发函数的执行
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))




# def counter(n):
#     print(‘start...‘)
#     i=0
#     while i < n:
#         yield i
#         i+=1
#     print(‘end...‘)
#
#
# g=counter(5)
# print(g)
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))








‘‘‘
yield的功能：
    1.相当于为函数封装好__iter__和__next__
    2.return只能返回一次值，函数就终止了，
    而yield能返回多次值，每次返回都会将函数暂停，下一次next会从
    上一次暂停的位置继续执行


‘‘‘
二 、表达式形式的yield的用途
#tail -f a.txt | grep ‘python‘


import time
def tail(filepath):
    with open(filepath,encoding=‘utf-8‘) as f:
        f.seek(0,2)
        while True:
            line=f.readline().strip()
            if line:
                yield line
            else:
                time.sleep(0.2)




# t=tail(‘a.txt‘)
#
# for line in t:
#     print(line)

def grep(pattern,lines):
    for line in lines:
        if pattern in line:
            yield line


g=grep(‘python‘,tail(‘a.txt‘))
print(g)

for i in g:
    print(i)

#grep -rl ‘python‘ /root


import os

def init(func):
    def wrapper(*args,**kwargs):
        res=func(*args,**kwargs)
        next(res)
        return res
    return wrapper

@init
def search(target):
    while True:
        search_path=yield
        g=os.walk(search_path)
        for par_dir,_,files in g:
            for file in files:
                file_abs_path=r‘%s\%s‘ %(par_dir,file)
                # print(file_abs_path)
                target.send(file_abs_path)

@init
def opener(target):
    while True:
        file_abs_path=yield
        # print(‘opener func==>‘,file_abs_path)
        with open(file_abs_path,encoding=‘utf-8‘) as f:
            target.send((file_abs_path,f))

@init
def cat(target):
    while True:
        file_abs_path,f=yield  #(file_abs_path,f)
        for line in f:
            tag=target.send((file_abs_path,line))
            if tag:
                break
@init
def grep(target,pattern):
    tag=False
    while True:
        file_abs_path,line=yield tag
        tag=False
        if pattern in line:
            tag=True
            target.send(file_abs_path)

@init
def printer():
    while True:
        file_abs_path=yield
        print(file_abs_path)



x=r‘C:\Users\Administrator\PycharmProjects\python17期\day5\a‘



g=search(opener(cat(grep(printer(),‘python‘))))
print(g)

g.send(x)

‘‘‘
面向过程的程序设计：是一种流水线式的编程思路，是机械式
优点：
    程序的结构清晰，可以把复杂的问题简单

缺点：
    1 扩展性差


应用场景：
    1 linux内核，git，httpd

‘‘‘

三、yield的另外一种用法

#yield的语句形式： yield 1
#yield的表达式形式： x=yield



#协程函数

def deco(func):
    def wrapper(*args,**kwargs):
        res=func(*args,**kwargs)
        next(res)
        return res
    return wrapper

@deco
def eater(name):
    print(‘%s ready to eat‘ %name)
    food_list=[]
    while True:
        food=yield food_list
        food_list.append(food)
        print(‘%s start to eat %s‘ %(name,food))


g=eater(‘alex‘)
# print(g)
# next(g) #等同于 g.send(None)

#

# g.send(‘手指头‘)
# g.send(‘脚指头‘)
# g.send(‘别人的手指头‘)
# g.send(‘别人的脚指头‘)

# print(g)
print(g.send(‘脚趾头1‘))
print(g.send(‘脚趾头2‘))
print(g.send(‘脚趾头3‘))




#x=yield
#g.send(‘1111‘),先把1111传给yield，由yield赋值给x
# 然后再往下执行，直到再次碰到yield，然后把yield后的返回值返回