在Python2.6上处理异常的正确方法

Question

I had an Python script that running continuously. If there any new file on directory then the python will open url using urllib2 to do some request on specific ip.

here are the code

encoded_string = base64.b64encode(image_file.read())
values = dumps({
    'image_data':encoded_string,
    'requestCode':'111'
})

headers = {"Content-Type": "application/json"}
request = Request("http:/xx.xxx.xx.xxx/api/carplate_service",data=values, headers=headers)
response = urlopen(request, timeout=60)

The code are working well but on random time, let say usually happened on 1-2 AM then I got this error:

<class 'urllib2.URLError'> - <urlopen error [Errno 110] Connection timed out>

I had an exception on that function on this bellow :

try:
    ip = sys.argv[1]
    histId = int(sys.argv[2])
    handler = ModHandler()
    wm = pyinotify.WatchManager()
    notifier = pyinotify.Notifier(wm, handler)
    wdd = wm.add_watch('./' + ip + '/', pyinotify.IN_CLOSE_WRITE)
    notifier.loop()
except BaseException as e:
    with open("error.log", "a") as text_file:
        exc_type, exc_obj, exc_tb = sys.exc_info()
        fname = os.path.split(exc_tb.tb_frame.f_code.co_filename)[1]
        text_file.write( time.strftime("%Y-%m-%d %H:%M:%S") + " [" + str(exc_tb.tb_lineno) + " - " + fname + "] : " + str(exc_type) + " - " +  str(e) + "\n")
        text_file.close();

The exception not working well because application cannot continue if there are some error like above.

My question are how to make program still continue even the exception throw?

I'm using python2.6

Thanks

Answer 1

For function calls that go out to external services I usually find that the following basic structure works pretty well

import time

expire_time = 2

while True:
    start_time = time.time()
    try:
        # Do something here
        # ....
        # If you make it to the bottom of the code, break out of the loop
        break
    except BaseException as e:
        # Compare the start_time with the current time
        now_time = time.time()
        if now_time > start_time + expire_time:
            raise e

        # Otherwise try executing the `try` block again

Using the code that you've provided it could look something like this

import time

expire_time = 2

while True:
    start_time = time.time()
    try:
        ip = sys.argv[1]
        histId = int(sys.argv[2])
        handler = ModHandler()
        wm = pyinotify.WatchManager()
        notifier = pyinotify.Notifier(wm, handler)
        wdd = wm.add_watch('./' + ip + '/', pyinotify.IN_CLOSE_WRITE)
        notifier.loop()
        break
    except BaseException as e:
        now_time = time.time()
        if now_time > start_time + expire_time:
            raise e
        else:
            with open("error.log", "a") as text_file:
                exc_type, exc_obj, exc_tb = sys.exc_info()
                fname = os.path.split(exc_tb.tb_frame.f_code.co_filename)[1]
                text_file.write( time.strftime("%Y-%m-%d %H:%M:%S") + " [" + str(exc_tb.tb_lineno) + " - " + fname + "] : " + str(exc_type) + " - " +  str(e) + "\n")
                text_file.close();