Python控制流程协程

Posted 2020-10-11

"""
# 16.2 用过协程的生成器的基本行为
#例子16-1 可能是协程最简单的使用演示
def simple_coroutine():
    print(‘-> coroiutine started‘)
    x = yield
    print(‘-> coroutine recived:‘,x)
my_coro = simple_coroutine()
print(my_coro)    #<generator object simple_coroutine at 0x10900f9e8>
#print(next(my_coro))
‘‘‘
-> coroiutine started
None
‘‘‘
#my_coro.send(42)
‘‘‘
-> coroutine recived: 42
StopIteration

‘‘‘
#【备注】协程可以身处四个状态中的一个。当前状态可以使用inspect.getgeneratorstate()函数确定，该函数会返回下述字符串中的一个。
#... ‘GEN_CREATED‘等待开始执行。  ‘GEN_RUNNING‘ 解释器正在执行  ‘GEN_SUSPENDED‘在yield表达式处暂停  ‘GEN_CLOSED‘执行结束。
#...因为send方法的参数会称为暂停的yield表达式的值，所以，仅当协程处于暂停状态时才能调用send方法。不过，如果协程还没激活（即，状态是‘GEN_CREATED‘），情况就不同了。因此，始终要调用next()激活协程-也可以调用my_coro.sen(None)，效果一样
#...如果创建协程对象后立即把None之外的值发给他，会出现下述错误：
my_coro = simple_coroutine()
my_coro.send(1729)  #TypeError: can‘t send non-None value to a just-started generator

# 例子16-2 产出两个值的协程
def simple_coro2(a):
    print(‘-> Started:a = ‘,a)
    b = yield a
    print(‘-> Received:b = ‘,b)
    c = yield (a+b)
    print(‘-> Received:c = ‘,c)
my_coro2 = simple_coro2(14)
from inspect import getgeneratorstate
print(getgeneratorstate(my_coro2))  #GEN_CREATED
print(next(my_coro2))
‘‘‘
-> Started:a =  14
14

‘‘‘
print(getgeneratorstate(my_coro2))  #GEN_SUSPENDED
print(my_coro2.send(28))
‘‘‘
-> Started:b =  28
42
‘‘‘
print(my_coro2.send(99))
‘‘‘
-> Received:c =  99
Traceback (most recent call last):
  File "/Users/suren/PycharmProjects/fluentPython/kongzhiliucheng/xiecheng.py", line 47, in <module>
    my_coro2.send(99)
StopIteration
‘‘‘
print(getgeneratorstate(my_coro2)) #‘GEN_CLOSED‘


#例子16-3 一个计算移动平均值的协程
def averager():
    total = 0.0
    count = 0
    average = None
    while True:#这个无限循环表明，只要调用方不断把值发给这个协程，它就会一直接收值，然后生成结果。仅当调用方在协程上调用.close()方法，或者没有对协程引用而被垃圾回收程序回收时，这个协程才终止
        term = yield average
        total += term
        count += 1
        average = total/count
coro_avg = averager()
print(next(coro_avg))  #None
print(coro_avg.send(10)) #10.0
print(coro_avg.send(30)) #20.0
print(coro_avg.send(5))  #15.0


#16.4 预激程序的装饰器
from functools import wraps

def coroutine(func):
    @wraps(func)
    def primer(*args,**kwargs):
        gen = func(*args,**kwargs)
        next(gen)
        return gen
    return primer

@coroutine
def averager():
    total = 0.0
    count = 0
    average = None
    while True:
        term = yield average
        total += term
        count += 1
        average = total/count

coro_avg = averager()
from inspect import getgeneratorstate
print(getgeneratorstate(coro_avg))  #GEN_SUSPENDED
print(coro_avg.send(10))     #10.0
print(coro_avg.send(30))    #20.0
print(coro_avg.send(5))     #15.0



#16.5 终止协程和异常处理
#例子 16-7 未处理的异常会导致协程终止
from functools import wraps
def coroutine(func):
    @wraps(func)
    def primer(*args,**kwargs):
        gen = func(*args,**kwargs)
        next(gen)
        return gen
    return primer

@coroutine
def averager():
    total = 0.0
    count = 0
    average = None
    while True:
        term = yield average
        total += term
        count += 1
        average = total/count
coro_avg = averager()
print(coro_avg.send(40))  #40.0
print(coro_avg.send(50))  #45.0
print(coro_avg.send(‘spam‘)) #TypeError: unsupported operand type(s) for +=: ‘float‘ and ‘str‘。此时，由于在协程里没有处理异常，协程会终止。如果试图重新激活协程，会抛出
print(coro_avg.send(60))  #不会处理


# 例子16-8 在协程中处理异常代码
class DemoException(Exception):
    ‘‘‘为这次演示定义的异常类型‘‘‘
def demo_exc_handling():
    print(‘-> coroutine started‘)
    while True:
        try:
            x = yield
        except DemoException:
            print(‘*** DemoException handled.Continuing...‘)
        else: #如果没有异常，则显示接收到的值
            print(‘->coroutine received:{!s}‘.format(x))
    raise RuntimeError(‘This line should never run.‘) #这一行永远不会执行，因为只有未处理的异常才会终止那个无限循环

#激活和关闭demo_exc_handling，没有异常
exc_coro = demo_exc_handling()
print(next(exc_coro))  #coroutine started
print(exc_coro.send(11)) #->coroutine received:11
print(exc_coro.send(22)) #->coroutine received:22
exc_coro.close()
from inspect import getgeneratorstate
print(getgeneratorstate(exc_coro))  #GEN_CLOSED

#把DemoException异常传入demo_exc_handling不会导致协程中止
exc_coro = demo_exc_handling()
print(next(exc_coro))  #-> coroutine started
print(exc_coro.send(11)) #->coroutine received:11
print(exc_coro.throw(DemoException))  #*** DemoException handled.Continuing...
print(getgeneratorstate(exc_coro))  #GEN_SUSPENDED

#如果无法处理传入的异常，协程会终止
exc_coro = demo_exc_handling()
print(next(exc_coro))  #-> coroutine started
print(exc_coro.send(11))
print(exc_coro.throw(ZeroDivisionError))
‘‘‘
Traceback (most recent call last):
  File "/Users/suren/PycharmProjects/fluentPython/kongzhiliucheng/xiecheng.py", line 172, in <module>
    print(exc_coro.throw(ZeroDivisionError))
  File "/Users/suren/PycharmProjects/fluentPython/kongzhiliucheng/xiecheng.py", line 145, in demo_exc_handling
    x = yield
ZeroDivisionError
‘‘‘
print(getgeneratorstate(exc_coro))  #GEN_CLOSED


#例子16-12 使用try/finally 块在协程终止时执行操作
class DemoException(Exception):
    ‘‘‘为这次演示定义的异常类型‘‘‘
def demo_finally():
    print(‘-> coroutine started‘)
    try:
        while True:
            try:
                x = yield
            except DemoException:
                print(‘*** DemoException handled.Continuing.....‘)
            else:
                print(‘-> coroutine received:{!s}‘.format(x))
    finally:
        print(‘->coroutine ending‘)

# 激活和关闭demo_exc_handling，没有异常
exc_coro = demo_finally() 
print(next(exc_coro))  #coroutine started  换行后打印 ->coroutine ending
print(exc_coro.send(11)) #->coroutine received:11  换行后打印 ->coroutine ending
print(exc_coro.send(22)) #->coroutine received:22  换行后打印 ->coroutine ending
exc_coro.close()
from inspect import getgeneratorstate
print(getgeneratorstate(exc_coro))  #GEN_CLOSED  换行后打印 ->coroutine ending

# 把DemoException异常传入demo_exc_handling不会导致协程中止
exc_coro = demo_finally()
print(next(exc_coro))  #-> coroutine started  换行后打印 ->coroutine ending
print(exc_coro.send(11)) #->coroutine received:11  换行后打印 ->coroutine ending
print(exc_coro.throw(DemoException))  #*** DemoException handled.Continuing...  换行后打印 ->coroutine ending
print(getgeneratorstate(exc_coro))  #GEN_SUSPENDED  换行后打印 ->coroutine ending

#如果无法处理传入的异常，协程会终止
exc_coro = demo_finally()
print(next(exc_coro))  #-> coroutine started  换行后打印 ->coroutine ending
print(exc_coro.send(11))
#print(exc_coro.throw(ZeroDivisionError))
‘‘‘
Traceback (most recent call last):
  File "/Users/suren/PycharmProjects/fluentPython/kongzhiliucheng/xiecheng.py", line 220, in <module>
    print(exc_coro.throw(ZeroDivisionError))
->coroutine ending
  File "/Users/suren/PycharmProjects/fluentPython/kongzhiliucheng/xiecheng.py", line 192, in demo_finally
    x = yield
ZeroDivisionError
->coroutine ending
‘‘‘
from inspect import getgeneratorstate
#print(getgeneratorstate(exc_coro))  #GEN_CLOSED  换行后打印 ->coroutine ending



#让协程返回值
#例子16-14 
from collections import namedtuple

Result = namedtuple(‘Result‘,‘count average‘)

def averager():
    total = 0.0
    count = 0
    average = None
    while True:
        term = yield
        if term is None:
            break
        total += term
        count += 1
        average = total/count
    return Result(count,average)

coro_avg = averager()
print(next(coro_avg)) #无产出
print(coro_avg.send(10)) #无产出
print(coro_avg.send(30)) #无产出
print(coro_avg.send(6.5)) #无产出
#print(coro_avg.send(None)) #StopIteration: Result(count=3, average=15.5)


#例子16-15
from collections import namedtuple
Result = namedtuple(‘Result‘,‘count average‘)

def averager():
    total = 0.0
    count = 0
    average = None
    while True:
        term = yield
        if term is None:
            break
        total += term
        count += 1
        average = total/count
    return Result(count,average)




coro_avg = averager()
print(next(coro_avg)) #无产出
print(coro_avg.send(10)) #无产出
print(coro_avg.send(30)) #无产出
print(coro_avg.send(6.5)) #无产出
try:
    coro_avg.send(None)
except StopIteration as exc:
    result = exc.value
print(result)  #Result(count=3, average=15.5)

"""