How python logging get it's configuration

Question

I used to Python logging, it works fine. The logging.basicConfig(...) set in one module (a some.py file), then we can use logging every where. Obviously, logging is global.

The question is how logging find it's settings, when we not call the module where basicConfig(...) appeared (in some.py file )? Is logging scan all the packages?

Even the logging.basicConfig(...) put into an any.py and the module (any.py) never get imported, or not used anywhere, the logging setting take effect!

Zaur Nasibov · Accepted Answer · 2012-04-04 07:46:52Z

4

To understand logging you have dive into Python's standard library sources.

Here is the trick:

#/usr/lib/python3.2/logging/__init__.py
...
root = RootLogger(WARNING)
Logger.root = root
Logger.manager = Manager(Logger.root)
...

# and 
def basicConfig(**kwargs):
    ...
        hdlr = StreamHandler(stream)
        fs = kwargs.get("format", BASIC_FORMAT)
        dfs = kwargs.get("datefmt", None)
        style = kwargs.get("style", '%')
        fmt = Formatter(fs, dfs, style)
        hdlr.setFormatter(fmt)
        root.addHandler(hdlr)

So, when you call basicconfig() with certain parameters, root logger is set. Finally getLogger:

def getLogger(name=None):
    """
    Return a logger with the specified name, creating it if necessary.

    If no name is specified, return the root logger.
    """
    if name:
        return Logger.manager.getLogger(name)
    else:
        return root

answered Apr 4, 2012 at 7:46

Zaur Nasibov

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1 Comment

Andrew_1510 Over a year ago

+1 for clear code samples. Still wondering when basicConfig get called.

Denis Ryzhkov · Accepted Answer · 2012-04-05 05:25:47Z

2

I think there is no magic scanning here.

Try to test it this way in a separate test directory:


test/main.py:
    import logging
    logging.info('test')

test/any.py:
    import logging
    logging.basicConfig(filename='test.log', level=logging.INFO)

python main.py

Result: NO test.log file.

Now let's update the test:


test/main.py:
    import logging
    import any
    logging.info('test')

python main.py

Result: new test.log file with INFO:root:test string inside.

So I guess that any.py in your case is imported somehow, despite your expectations.

You may find the way any.py is imported easily, just add few lines there:
```
test/any.py:
    from traceback import print_stack
    print_stack()
    ...

python main.py
```
Result:
```
File "main.py", line 2, in 
    import any
File "any.py", line 2, in 
    print_stack()
```
This stack shows that any.py is imported from main.py.

I hope you will find where it is imported from in your case.

answered Apr 5, 2012 at 5:25

Denis Ryzhkov

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1 Comment

Andrew_1510 Over a year ago

Yes, no magics happens when it put into a new place. In my old project, I do put the logging setting logging.basicConfig() into a new and not-used file, and it do show up. Only thing possible to scan the file is the testing tool, pytest in case.

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