Python Logging for Humans
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.
lggr Bump version for new release. Jun 13, 2016
.gitignore Adds setup.cfg and for PYPI Aug 3, 2012
LICENSE.txt Update README to stop referencing .shutdown(). Dec 3, 2012
setup.cfg Bump version. May 4, 2013

Lggr - Python Logging For Humans

Have you ever tried to do anything with the python logging module?

I have. I didn't like it at all. The API was very confusing. Instead of dealing with all of its intricacies, I decided to roll my own.

I've been inspired by dabeaz's presentation on coroutines and Kenneth Reitz's presentation on better python libraries.


pip install lggr

How does it work?

Create a logger object.

import lggr
mylggr = lggr.Lggr()

Add a coroutine (or any function or object with send and close methods) to consume log messages. lggr includes some default ones:

  • lggr.Printer() writes to stdout
  • lggr.StderrPrinter() writes to stderr
  • lggr.Printer(filepath) opens a file at filepath and writes to that.
  • lggr.SocketWriter(host, port) writes to a network socket
  • lggr.Emailer(recipients) sends emails
  • lggr.GMailer(recipients, gmail_username, gmail_password, subject="optional") also sends emails, but does it from Gmail which is way sexier than doing it from your own server.

You can choose to add different coroutines to different levels of logging. Maybe you want to receive emails for all of your critical messages, but only print to stderr for everything else.

mylggr.add(mylggr.ALL, lggr.Printer()) # mylggr.ALL is a shortcut to add a coroutine to all levels
mylggr.add(mylggr.CRITICAL, lggr.Emailer(""))

Do some logging."Hello, world!")
mylggr.warning("Something seems to have gone {desc}", {"desc":"amuck!"})
mylggr.critical("Someone {} us {} the {}!", "set", "up", "bomb")
mylggr.close() # stop logging

What kind of information can I log?

Anything you want. Log messages are created using str.format, so you can really create anything you want. The default format includes access to the following variables:

  • asctime = time as a string (from time.asctime())
  • code = the exact code that called the logging function
  • codecontext = surrounding 10 lines surrounding code
  • defaultfmt = the default format of a log message
  • excinfo = execution information, either passed in or
  • filename = filename the logging function was called from (
  • funcname = the function name
  • levelname = level of logging as a string ("INFO")
  • levelno = level of logging as an integer (0)
  • lineno = the line number
  • logmessage = the user's formatted message
  • messagefmt = the format string to be used to create the log message
  • module = module the logging function was called from (in this case, None)
  • pathname = path to the file that the logging function was called from (~/
  • process = current process id
  • processname = name of the current process, if multiprocessing is available
  • stackinfo = stack information, created if the optional inc_stackinfo argument is True (it defaults to False if not explicitly passed) or the logging function is called with instance functions critical, debug, or error.
  • threadid = the thread id, if the threading module is available
  • threadname = the thread name, if the threading module is available
  • time = time as seconds from epoch (from time.time())

If you want to use any extra information, simply pass in a dict with the named argument extra:

>>> mylggr.config['defaultfmt'] = '{name} sez: {logmessage}'
>>>"This is the {}", "message", extra={"name":"Peter"})
Peter sez: This is the message

Something to be careful about: internally, lggr uses the older (2.0+) python format syntax to be compatible with older versions. As of 2.7, you can call '{} {} {}'.format(1, 2, 3), but this will break for earlier versions. When making calls to lggr, make sure that you use the correct syntax for your version of Python. If your program will run on multiple different versions, then it would probably best to use the older style ('{0} {1} {2}'.format(1, 2, 3)).

A stackinfo example

stackinfo is cool because it lets you do really helpful tracebacks to where exactly your logging function is being called. For example, with some Lggr mylggr, I could run the following:

mylggr.config['defaultfmt'] = '{asctime} ({levelname}) {logmessage}\nIn {pathname}, line {lineno}:\n{codecontext}'

def outer(a):
    def inner(b):
        def final(c):
            mylggr.critical("Easy as {}, {}, {}!", a, b, c)
        return final
    return inner



Sun Nov 11 14:43:38 2012 (CRITICAL) Easy as a, b, c!
In bin/, line 29:
| old = mylggr.config['defaultfmt']
| mylggr.config['defaultfmt'] = '{asctime} ({levelname}) {logmessage}\nIn {pathname}, line {lineno}:\n{codecontext}'
| def outer(a):
|   def inner(b):
|     def final(c):
>       mylggr.critical("Easy as {}, {}, {}!", a, b, c)
|     return final
|   return inner
| outer(1)(2)(3)

Is it robust?

Not yet. It's definitely still in the early days, so use at your own risk. I wouldn't put this into production right now, but it's been working fine for my toy projects. Please submit any bugs you find to the github tracker!

Also, for the risk-averse, it ignores all errors when calling the .log(...) method. So if you seriously mess up, the worst thing that can happen is that you won't see a log message. For the less risk-averse, this can be overridden when the Lggr object is created.

What's next?

I'm still working on text-sending and IRC/IM-writing log functions - maybe one of you could help?

Also, I've sort of ignored the Unicode problem entirely. That needs to change.

I'd also like to add serialization / loading of both Lggr objects and their configurations, for easier saving / loading.

Who did this?

Peter Downs.