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

Question

Here is what I am doing

>>> 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 >>>  

My python version is

$ python --version Python 2.7.3 

How do I make it work?

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.

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.