How can I get formatter string from a logging.formatter object in Python?

Question

I want to make a logging manager gui. Basically I want to get the tree structure of loggers and show their level and formatter in a pyqt gui. How can I get the format string from a formatter associated a handler object?

eg:

import logging
_logger = logging.getLogger('myLogger')

ch = logging.StreamHandler()
ch.setLevel(logging.INFO)
formatter = logging.Formatter('%(name)s:%(levelname)s: %(message)s')
ch.setFormatter(formatter)
_logger.addHandler(ch)
_logger.propagate=0

Now I have the _logger, how can I get string '%(name)s:%(levelname)s: %(message)s' from the logging.Formatter object?

>>> _logger.handlers[0]
<logging.StreamHandler object at 0x13807610>
>>> _logger.handlers[0].formatter
<logging.Formatter object at 0x13807690>

Martijn Pieters · Accepted Answer · 2023-06-14 09:29:55Z

36

logging.Formatter instances have a _fmt attribute:

>>> _logger.handlers[0].formatter
<logging.Formatter object at 0x102c72fd0>
>>> _logger.handlers[0].formatter._fmt
'%(name)s:%(levelname)s: %(message)s'

You can always use dir() and vars() on objects to see what names might be available:

>>> vars(_logger.handlers[0].formatter)
{'_style': <logging.PercentStyle object at 0x102e6bbf0>, '_fmt': '%(name)s:%(levelname)s: %(message)s', 'datefmt': None}

or you could just look at the source code (linked from the top of the module documentation).

edited Jun 14, 2023 at 9:29

answered Jul 16, 2016 at 17:21

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

PaulMcG Over a year ago

If accessing an internal _ attribute (which is generally a frowned-upon practice) is good enough for a million-pointer, it is good enough for me.

Martijn Pieters Over a year ago

@PaulMcG: the logging module is breaking style conventions in so many ways already, and there is no other option to access the format string. Needs must!

Martijn Pieters Over a year ago

@PaulMcG: the _ initial underscore convention is more of a warning: Watch out, this attribute could be removed or change meaning in a future version without notice. With the logging module however, I'm quite confident that if the attribute were ever to go away that there'd be a long deprecation period first, given the history of the package.

PaulMcG Over a year ago

This comment was as much for my own benefit as for anyone else; I recently wrote code that accessed this _fmt field so that I could define a new formatter with some custom placeholders to it. 20 years' worth of Python coding habits gave me pause at committing such an act, but now I know I am in good company.

Collectives™ on Stack Overflow

How can I get formatter string from a logging.formatter object in Python?

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related