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!

Answer 1

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