"TIP: Don’t use f-strings in logging statements" - not true (or more context needed)

[xavdid]

Location within the Book

• Chapter or Appendix: 29
• Section: 3
• Subsection: 5

Description

The book includes a "TIP" box saying that:

As of Python 3.9, f-strings don’t work with loggers.

I don't believe this info box is accurate, nor was I able to find a source for that. I also did a (very basic) test to check:

# tested on both 3.9.10 and 3.10.0
import logging
l = logging.getLogger()
l.addHandler(logging.StreamHandler())
a = 3

l.error(f'a is {a}')
# prints "a is 3"

Possible Solutions

I think either:

• the box is right and my little snippet works while actual logging doesn't
• the box is mistaken and should be removed (or updated to say "as of version X.Y.Z, f-strings work in loggers")

Your full name so we can provide accurate credit within the book

David Brownman

[strokirk]

The good example could also be improved:

logger.debug('Only %d pints of ice cream left.' % pints_remaining)

This uses interpolation of the log message, but it's better practise to allow the logging module to do that interpolation for you.

logger.debug('Only %d pints of ice cream left.', pints_remaining)

There is a great flake8 plugin to check this automatically: https://github.com/globality-corp/flake8-logging-format