Python，重新进入`with`块

Question

I am currently working on an import script that import listings from a database that regularly shuts down every 15 mins for re-snap.

I have created a with block as below to look after the retry mechanism when creating connections:

class DBRetryController(object):
    conn_obj = None
    connection = None
    cursor = None
    retry_count_down = None
    sleep_time = None

    def __init__(self, conn_obj, retry_count_down=5, sleep_time=10):
        self.conn_obj = conn_obj
        self.retry_count_down = retry_count_down
        self.sleep_time = sleep_time

    def __enter__(self):
        ex = None
        while self.retry_count_down > 0:
            try:
                if hasattr(self.conn_obj, '__call__'):
                    self.connection = self.conn_obj()
                else:
                    self.connection = self.conn_obj
                self.cursor = self.connection.cursor()
                self.retry_count_down = False
            except OperationalError as ex:
                log.warning('Caught db error, possibly due to sql server gone away, retrying in a few moment')
                self.retry_count_down -= 1
                time.sleep(self.sleep_time)
        if ex:
            raise ex
        return self.connection, self.cursor

    def __exit__(self, type, value, traceback):
        try:
            self.cursor.close()
            self.connection.close()
        except:
            pass

        if value:
            raise value

And use as below:

with DBRetryController(self.connection) as (_, cursor):
    cursor.execute(self.LISTING_QUERY)

But the problem is the server can shutdown during execution of the query, is it possible to modifying the DBRetryController to make the nested block of code to re-enter?

Answer 1

If I understand your question correctly, I think you can use such a scheme:

notCompleted = 1
class TestClass():
    def run(self):
        global notCompleted
        notCompleted = 1
        #do_something here
        notCompleted = 0


test =  TestClass()
test.run()
while(notCompleted):
    test.run()

Let assume that I want to be sure, even if any error occure during execution of run() method, my program will retry to finish to run it complete again. The notCompleted is 1 by default. when I call the run method at the beginning I assign 1 to it and at the end of my run method I assigned 0 to it. Anywhere inside the run() if I have any problem, in the while loop the function will called again.

I think you need to add a Try...Catch too.