I am trying to learn how an application works. And for this I am inserting debug commands as the first line of each function’s body with the goal of logging the function’s name as well as the line number (within the code) where I send a message to the log output. Finally, since this application comprises of many files, I want to create a single log file so that I can better understand the control flow of the application.
Here is what I know:
for getting function name, I can use
function_name.__name__
but I don’t want to use the function_name (so that I could rapidly copy and paste a genericLog.info("Message")
in the body of all functions). I know this could be done in C using__func__
macro but I am not sure about python.for getting the filename and line number, I have seen that (and I believe that) my application is using Python
locals()
function but in a syntax that I am not completely aware of e.g.:options = "LOG.debug('%(flag)s : %(flag_get)s' % locals())
and I tried it using likeLOG.info("My message %s" % locals())
which produces something like{'self': <__main__.Class_name object at 0x22f8cd0>}
. Any input on this please?I know how to use logging and add handler to it to log to a file but I am not sure if a single file can be used to record all log messages in correct order of function calls in the project.
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Answer
You have a few marginally related questions here.
I’ll start with the easiest: (3). Using logging
you can aggregate all calls to a single log file or other output target: they will be in the order they occurred in the process.
Next up: (2). locals()
provides a dict of the current scope. Thus, in a method that has no other arguments, you have self
in scope, which contains a reference to the current instance. The trick being used that is stumping you is the string formatting using a dict as the RHS of the %
operator. "%(foo)s" % bar
will be replaced by whatever the value of bar["foo"]
is.
Finally, you can use some introspection tricks, similar to those used by pdb
that can log more info:
def autolog(message): "Automatically log the current function details." import inspect, logging # Get the previous frame in the stack, otherwise it would # be this function!!! func = inspect.currentframe().f_back.f_code # Dump the message + the name of this function to the log. logging.debug("%s: %s in %s:%i" % ( message, func.co_name, func.co_filename, func.co_firstlineno ))
This will log the message passed in, plus the (original) function name, the filename in which the definition appears, and the line in that file. Have a look at inspect – Inspect live objects for more details.
As I mentioned in my comment earlier, you can also drop into a pdb
interactive debugging prompt at any time by inserting the line import pdb; pdb.set_trace()
in, and re-running your program. This enables you to step through the code, inspecting data as you choose.