python - try block 在无限 while 循环中导致线程退出

Question

我正在开发一个 Python 程序，该程序使用线程无限读取串行连接并根据输入处理异常。

本质上:在一个线程中，我想永远做某事，如果发生某些事情则引发异常，从异常返回并继续永远做某事，同时处理任何 future 的异常。

我创建了一个测试程序来使用 time.sleep() 模拟此行为，以隔离我的问题。

import threading
import time

class TimeError(Exception):
    def __init__(self, mesg):
        self.mesg=mesg

class myObject(object):

    def __init__(self):
        self.threadRunning=False

    def my_thread(self):
        threadCount=0

        try:
            while True:
                time.sleep(1)

                print "Child: {}".format(threadCount)
                threadCount = threadCount + 1
                if threadCount>=5:
                    raise TimeError("5 seconds elapsed!")

        except TimeError as e:
            print (e.mesg)

        print "Exiting thread!"
        self.threadRunning=False

    def my_parent(self): #start thread and wait
        childThread = threading.Thread(target=self.my_thread)
        childThread.daemon = True

        childThread.start()
        self.threadRunning = True

        parentCount=0
        while (self.threadRunning == True):
            print "Parent: {}".format(parentCount)
            parentCount = parentCount + 1
            time.sleep(1)

        print "Program complete."


fooObject = myObject()
fooObject.my_parent()

我收到的输出是

Parent: 0
Child: 0
Parent: 1
Child: 1
 Parent: 2
Child: 2
 Parent: 3
Child: 3
 Parent: 4
Child: 4
5 seconds elapsed!
Exiting thread!
 Parent: 5
Program complete.

我对 Python 和异常的使用相当陌生(我的背景是 C)。据我了解，异常用于调试正常执行流程中的异常并从中恢复。我读到它是 unwise to throw your own Exceptions ，但对于我的最终申请，我必须这样做。

那么，在处理线程中的异常后如何回到 While True 无限循环？我想继续增加 threadCount 并处理异常，而不是退出线程。

Answer 1

通过简化我的代码来提出这个问题，我找到了解决方案。

简而言之，while True 循环应该围绕 try/except block ，而不是相反。这是因为...

If an exception occurs during execution of the try clause, the rest of the >clause is skipped. Then if its type matches the exception named after the >except keyword, the except clause is executed, and then execution continues >after the try statement.

https://docs.python.org/2/tutorial/errors.html#handling-exceptions

我的假设是，异常的行为类似于中断，因为它会执行处理代码，然后返回到引发异常后的执行点。这不是C...

固定代码:

import threading
import time

class TimeError(Exception):
    def __init__(self, mesg):
        self.mesg=mesg

class myObject(object):

    def __init__(self):
        self.threadRunning=False

    def my_thread(self):
        threadCount=0


        while True:
            try:
                time.sleep(1)

                print "Child: {}".format(threadCount)
                threadCount = threadCount + 1
                if threadCount>=5:
                    raise TimeError("5 seconds elapsed!")

            except TimeError as e:
                print (e.mesg)

        print "Exiting thread!"
        self.threadRunning=False

    def my_parent(self): #start thread and wait
        childThread = threading.Thread(target=self.my_thread)
        childThread.daemon = True

        childThread.start()
        self.threadRunning = True

        parentCount=0
        while (self.threadRunning == True):
            print "Parent: {}".format(parentCount)
            parentCount = parentCount + 1
            time.sleep(1)

        print "Program complete."


fooObject = myObject()
fooObject.my_parent()

预期输出:

Parent: 0
Child: 0
Parent: 1
Child: 1
Parent: 2
Child: 2
Parent: 3
Child: 3
Parent: 4
Child: 4
 5 seconds elapsed!
Parent: 5
Parent: 6
 Child: 5
5 seconds elapsed!
Child: 6
 5 seconds elapsed!
Parent: 7
Parent: 8
 Child: 7
5 seconds elapsed!
Child: 8
 5 seconds elapsed!
...indefinately