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Introspect and display the logger tree inside "logging"

Project description

Introspection for the logging logger tree in the Standard Library.

You can install this package with the standard pip command:

$ pip install logging_tree

While you can write programs that call this package’s tree() function and examine the hierarchy of logger objects that it finds inside of the Standard Library logging module, the simplest use of this package for debugging is to call printout() to print the loggers, filters, and handlers that your application has configured:

>>> logging.getLogger('a')
>>> logging.getLogger('a.b').setLevel(logging.DEBUG)
>>> logging.getLogger('x.c')
>>> from logging_tree import printout
>>> printout()
   Level WARNING
   |   Level NOTSET so inherits level WARNING
   |   |
   |   o<--"a.b"
   |       Level DEBUG
           Level NOTSET so inherits level WARNING

If you instead want to write the tree diagram to a file, stream, or other file-like object, use:


The logger tree should always print successfully, no matter how complicated. A node whose [name] is in square brackets is a “place holder” that has never actually been named in a getLogger() call, but was created automatically to serve as the parent of loggers further down the tree.

There are several interfaces that logging_tree supports, depending on how much detail you need.


Prints the current logger tree, or the tree based at the given node, to the standard output.


Builds and returns the multi-line description of the current logger tree, or the tree based at the given node, as a single string with newlines inside and a newline at the end.


A generator that yields a series of lines that describe the tree based at the given node. Note that the lines are returned without newline terminators attached.


Fetch the current tree of loggers from the logging module. Returns a node, that is simply a tuple with three fields:

[0] the logger name ("" for the root logger).
[1] the logging.Logger object itself.
[2] a list of zero or more child nodes.

I welcome contributions and ideas as this package matures. You can find the bug tracker at the repository page on github. Developers can run this package’s tests with:

$ python -m unittest discover logging_tree

On older versions of Python you will instead have to install unittest2 and use its unit2 command line tool to run the tests.


Version 1.9 - 2021 April 10

Declare compatibility with Python 3.9. Improve how the logging module’s built-in Formatter class is displayed under old Python versions where the logging module uses old-style classes.

Version 1.8.1 - 2020 January 26

Adjust one test to make it pass under Python 3.8, and update the distribution classifiers to declare compatibility with Python versions through 3.8.

Version 1.8 - 2018 August 5

Improve the output to better explain what happens if a “parent” attribute has been set to None.

Version 1.7 - 2016 January 23

Detect whether each logger has the correct “parent” attribute and, if not, print where its log messages are being sent instead.

Version 1.6 - 2015 January 8

Fixed a crash that would occur if a custom logging Formatter was missing its format string attributes.

Version 1.5 - 2014 December 24

Handlers now display their logging level if one has been set, and their custom logging formatter if one has been installed.

Version 1.4 - 2014 January 8

Thanks to a contribution from Dave Brondsema, disabled loggers are now actually marked as “Disabled” to make it less of a surprise that they fail to log anything.

Version 1.3 - 2013 October 29

Be explicit and display the logger level NOTSET along with the effective level inherited from the logger’s ancestors; and display the list of .filters of a custom logging handler even though it might contain custom code that ignores them.

Version 1.2 - 2013 January 19

Compatible with Python 3.3 thanks to @ralphbean.

Version 1.1 - 2012 February 17

Now compatible with 2.3 <= Python <= 3.2.

Version 1.0 - 2012 February 13

Can display the handler inside a MemoryHandler; entire public interface documented; 100% test coverage.

Version 0.6 - 2012 February 10

Added a display format for every logging.handlers class.

Version 0.5 - 2012 February 8

Initial release.

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