Showing the right funcName when wrapping logger functionality in a custom class

Question

This is the formatting string that I am using for logging:

\'%(asctime)s - %(levelname)-10s - %(funcName)s - %(message)s\'

But to show the logg

Answer 1

Thanks to @cygnusb and the others who already provided useful pointers. I chose to use the Python 3.4 Logger.findCaller method as my starting point. The following solution has been tested with Python 2.7.9 and 3.4.2. This code is meant to be placed in its own module. It produces the correct answer with only one iteration of the loop.

import io
import sys

def _DummyFn(*args, **kwargs):
    """Placeholder function.

    Raises:
        NotImplementedError
    """
    _, _ = args, kwargs
    raise NotImplementedError()

# _srcfile is used when walking the stack to check when we've got the first
# caller stack frame, by skipping frames whose filename is that of this
# module's source. It therefore should contain the filename of this module's
# source file.
_srcfile = os.path.normcase(_DummyFn.__code__.co_filename)
if hasattr(sys, '_getframe'):
    def currentframe():
        return sys._getframe(3)
else:  # pragma: no cover
    def currentframe():
        """Return the frame object for the caller's stack frame."""
        try:
            raise Exception
        except Exception:
            return sys.exc_info()[2].tb_frame.f_back

class WrappedLogger(logging.Logger):
    """Report context of the caller of the function that issues a logging call.

    That is, if

        A() -> B() -> logging.info()

    Then references to "%(funcName)s", for example, will use A's context
    rather than B's context.

    Usage:
        logging.setLoggerClass(WrappedLogger)
        wrapped_logging = logging.getLogger("wrapped_logging")
    """
    def findCaller(self, stack_info=False):
        """Return the context of the caller's parent.

        Find the stack frame of the caller so that we can note the source
        file name, line number and function name.

        This is based on the standard python 3.4 Logger.findCaller method.
        """
        sinfo = None
        f = currentframe()
        # On some versions of IronPython, currentframe() returns None if
        # IronPython isn't run with -X:Frames.
        if f is not None:
            f = f.f_back

        if sys.version_info.major == 2:
            rv = "(unknown file)", 0, "(unknown function)"
        else:
            rv = "(unknown file)", 0, "(unknown function)", sinfo

        while hasattr(f, "f_code"):
            co = f.f_code
            filename = os.path.normcase(co.co_filename)
            if filename == _srcfile or filename == logging._srcfile:
                f = f.f_back
                continue
            # We want the frame of the caller of the wrapped logging function.
            # So jump back one more frame.
            f = f.f_back
            co = f.f_code
            if sys.version_info.major == 2:
            rv = "(unknown file)", 0, "(unknown function)"
        else:
            rv = "(unknown file)", 0, "(unknown function)", sinfo

        while hasattr(f, "f_code"):
            co = f.f_code
            filename = os.path.normcase(co.co_filename)
            if filename == _srcfile or filename == logging._srcfile:
                f = f.f_back
                continue
            # We want the frame of the caller of the wrapped logging function.
            # So jump back one more frame.
            f = f.f_back
            co = f.f_code
            if sys.version_info.major == 2:
                rv = co.co_filename, f.f_lineno, co.co_name
            else:
                if stack_info:
                    sio = io.StringIO()
                    sio.write('Stack (most recent call last):\n')
                    traceback.print_stack(f, file=sio)
                    sinfo = sio.getvalue()
                    if sinfo[-1] == '\n':
                        sinfo = sinfo[:-1]
                    sio.close()
                rv = co.co_filename, f.f_lineno, co.co_name, sinfo
            break

        return rv

Answer 2

As suggested in the first answer, subclassing the Logger class and using logging.setLoggerClass should do the trick. You will need a modified findCaller function, that is handling your wrapped function call(s).

Put the following into a module, since the findCaller class method is searching the first call from a file, which is not the current source filename.

import inspect
import logging
import os

if hasattr(sys, 'frozen'): #support for py2exe
    _srcfile = "logging%s__init__%s" % (os.sep, __file__[-4:])
elif __file__[-4:].lower() in ['.pyc', '.pyo']:
    _srcfile = __file__[:-4] + '.py'
else:
    _srcfile = __file__
_srcfile = os.path.normcase(_srcfile)

class WrappedLogger(logging.Logger):
    def __init__(self,name):
        logging.Logger.__init__(self, name)

    def findCaller(self):
        """
        Find the stack frame of the caller so that we can note the source
        file name, line number and function name.
        """
        # get all outer frames starting from the current frame
        outer = inspect.getouterframes(inspect.currentframe())
        # reverse the order, to search from out inward
        outer.reverse()
        rv = "(unknown file)", 0, "(unknown function)"    

        pos = 0
        # go through all frames
        for i in range(0,len(outer)):
            # stop if we find the current source filename
            if outer[i][1] == _srcfile:
                # the caller is the previous one
                pos=i-1
                break

        # get the frame (stored in first tuple entry)
        f = outer[pos][0]

        co = f.f_code
        rv = (co.co_filename, f.f_lineno, co.co_name)

        return rv
# Usage:
logging.setLoggerClass(WrappedLogger)
log = logging.getLogger("something")