Python: Logging TypeError: not all arguments converted during string formatting

Question

Here is a quick reproduction of the issue:

>>> import logging
>>> logging.getLogger().setLevel(logging.INFO)
>>> from datetime import date
>>> date = date.today()
>>> logging.info('date={}', date)
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 846, in emit
    msg = self.format(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 723, in format
    return fmt.format(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 464, in format
    record.message = record.getMessage()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 328, in getMessage
    msg = msg % self.args
TypeError: not all arguments converted during string formatting
Logged from file <stdin>, line 1
>>>

How do I make it work?

_{This is effectively a special case of Why do I get "TypeError: not all arguments converted during string formatting" trying to substitute a placeholder like {0} using %? – but because the actual formatting step happens outside the user’s code, different workarounds are necessary.}

Asked By: daydreamer

||

Source

Answer 1

You cannot use new-style formatting when using the logging module; use %s instead of {}.

logging.info('date=%s', date)

The logging module uses the old-style % operator to format the log string. See the debug method for more detail.

If you really want to use str.format() string formatting, consider using custom objects that apply the formatting ‘late’, when actually converted to a string:

class BraceMessage(object):
    def __init__(self, fmt, *args, **kwargs):
        self.fmt = fmt
        self.args = args
        self.kwargs = kwargs

    def __str__(self):
        return self.fmt.format(*self.args, **self.kwargs)

__ = BraceMessage

logging.info(__('date={}', date))

This is an approach the Python 3 logging module documentation proposes, and it happens to work on Python 2 too.

Answered By: Martijn Pieters

Answer 2

You could do the formatting yourself:

logging.info('date={}'.format(date))

As was pointed out by Martijn Pieters, this will always run the string formatting, while using the logging module would cause the formatting to only be performed if the message is actually logged.

Answered By: Matt

Answer 3

Martijn’s answer is correct, but if you prefer to use new style formatting with logging, it can be accomplished by subclassing Logger.

import logging

class LogRecord(logging.LogRecord):
    def getMessage(self):
        msg = self.msg
        if self.args:
            if isinstance(self.args, dict):
                msg = msg.format(**self.args)
            else:
                msg = msg.format(*self.args)
        return msg

class Logger(logging.Logger):
    def makeRecord(self, name, level, fn, lno, msg, args, exc_info, func=None, extra=None):
        rv = LogRecord(name, level, fn, lno, msg, args, exc_info, func)
        if extra is not None:
            for key in extra:
                rv.__dict__[key] = extra[key]
        return rv

Then just set the logging class:

logging.setLoggerClass(Logger)

Answered By: Jeff-Meadows

Answer 4

You could do also (Python 3);

logging.info(f'date={date}')

Answered By: yusuf

Python: Logging TypeError: not all arguments converted during string formatting

Question:

Answers: