Per-file/module logger in Python

Question

I have some Python code I need to add logging to. I've always preferred nice big C macro looking statements like "DEBUG()", "ERROR()", etc for logging. I feel it makes the code easier to read (no objects) when trace-points are visually differentiable from the actual code. I also would like to be able to set logging levels at a per-module level. How could I make a module called "log" that is capable of doing this (while making use of the Python std library logging module)? E.g.: File: main.py ``` # This imports LOG_MODULE_NAME, DEBUG, WARN, etc from log import * import my_module LOG_MODULE_NAME("main") log.set_level("main", log.LVL_DEBUG) log.set_level("my_module", log.LVL_WARN) if __name__ == "__main__": foo = my_module.myFunc(2) DEBUG("Exiting main.py") ``` File: my_module.py ``` from log import * LOG_MODULE_NAME("my_module") def myFunc(x): DEBUG("Entering function") if x != 1: WARN("I thought it would be 1") DEBUG("Exiting function") return x+1 ``` I'd expect output to look somethin…

Accepted Answer

If you want to have the logger's name indicate the module in which it was used, you can use the `logger.getLogger([name])` module function, and pass `__name__` as its (optional) argument, as explained here.

If you want to use names like `DEBUG()`, do something like this in each of your files...

```
LOG_MODULE_NAME = logging.getLogger(__name__)

def DEBUG(msg):
    global LOG_MODULE_NAME
    LOG_MODULE_NAME.debug(msg)
```

I am not clear on the way that global namespaces actually work in Python... this answer says

each module has its own "global" namespace.

So I guess you will be just fine like that, since `LOG_MODULE_NAME` won't collide between modules.

I believe that this approach will give you one logfile, where the lines will look like this:

```
DEBUG:my_module:Entering function
WARN:my_module:I thought it would be 1
DEBUG:my_module:Exiting function
DEBUG:root:Exiting main.py
```

Not instrospective enough? You want the `inpsect` module, which will give you a lot of information about the program while it's running. This will, for instance, get you the current line number.

Your note about "setting log levels at a per-module level" makes me think that you want something like `getEffectiveLevel()`. You could try to smush that in like this:

```
LOG_MODULE_NAME = logging.getLogger(__name__)
MODULE_LOG_LEVEL = log.LVL_WARN

def DEBUG(msg):
    if MODULE_LOG_LEVEL = log.LVL_DEBUG:
        global LOG_MODULE_NAME
        LOG_MODULE_NAME.debug(msg)
```

I'm not experienced enough with the `logging` module to be able to tell you how you might be able to make each module's log change levels dynamically, though.

Per-file/module logger in Python

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