Logging messages appear twice in console Python

Question

I have found this answer to a seemingly similar issue, however (since I'm novice into Python) I am not sure how to implement this solution in my code (if it's the same issue after all).

In my code I have the following section:

logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
                    filename='C:\\Tests\\TRACE.log',
                    filemode='a')
console = logging.StreamHandler()
console.setLevel(logging.INFO)
consoleFormatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
console.setFormatter(consoleFormatter)
logging.getLogger('').addHandler(console)
localLog = logging.getLogger('text')

The funny thing is that it used to work fine but at some moment it started writing these duplicate messages to console.

Could someone give me a direction here please?

Answer 1

Typically duplicate log statements occur because there are two separate handlers attached that are directing your log statements to the same place. There are a couple of things worth trying to get to the root of the problem:

1. Comment out the call to logging.basicConfig - if this eliminates the duplicate log statements then this means it is likely that you don't need to manually configure the second log handler.
2. If you are using an IDE, it may be worth putting a breakpoint onto a log statement, and stepping in using the debugger so you can introspect the state of pythons log setup to get a clearer picture of what different handlers are attached.

To make your logging easier to manage, it may be worth looking to move the configuration out of the code and into a configuration file - the Python document on logging configuration is a great place to start.

Answer 2

It seems that I have figured out the source of this problem.

The thing is that I used to get logger at module level. It looked pretty logical but there is a pitfall – Python logging module respects all created logger before you load the configuration from a file. So basically, when I was importing a module(which uses gets logger internally) to a main code(where I was calling for a logger as well) it resulted in streaming the logger data twice.

The possible solutions to this problem are:

1. Do not get logger at the module level
2. Set disable_existing_loggers to False. Added since Python 2.7