Lazy log formatter

Pre-commit hook to automatically detect and convert f-strings in Python code to printf-style logging calls, following W1203 Pylint rule:

https://pylint.readthedocs.io/en/stable/user_guide/messages/warning/logging-fstring-interpolation.html

Usage

To use it with pre-commit, add the following lines to your .pre-commit-config.yaml:

- repo: https://github.com/dmar1n/lazy-log-formatter
  rev: 0.6.2
  hooks:
    - id: lazy-log-formatter
      args: ['--fix']

Options

• --fix: Automatically fix f-strings used in log calls to lazy log calls.
• DIR [DIR ...]: One or more directories to search for Python files. If not specified, defaults to the current directory.

Examples

Check all Python files in the current directory and subdirectories:

python -m src.cli

Check all Python files in two directories:

python -m src.cli src/ tests/

Fix issues in all Python files in a directory:

python -m src.cli mydir --fix

If the --fix option is used, the hook will convert f-strings in log calls to lazy log calls, as follows:

# Before
logger.info(f'Hello {name}')

# After
logger.info('Hello %s', name)

# Before
logger.info(f'Hello {name} {surname}')

# After
logger.info('Hello %s %s', name, surname)

Example in a Python class

import logging
from datetime import datetime


def log_and_return_datetime():
    now = datetime.now()
    logging.info(f"Current datetime: {now}")
    return now


class DateTimeLogger:
    def __init__(self):
        self._logger = logging.getLogger(self.__class__.__name__)

    def log_datetime(self):
        now = datetime.now()
        self._logger.info(f"Current datetime: {now}")
        return now

python src\cli.py tests\data

The output will be:

F-string in logging call at ...\tests\data\test.py:8: f'Current datetime: {now}'
F-string in logging call at ...\tests\data\test.py:18: f'Current datetime: {now}'
F-strings found and fixed in '...\tests\data\test.py'.

After running the formatter, the code will be transformed to:

import logging
from datetime import datetime


def log_and_return_datetime():
    now = datetime.now()
    logging.info("Current datetime: %s", now)
    return now


class DateTimeLogger:
    def __init__(self):
        self._logger = logging.getLogger(self.__class__.__name__)

    def log_datetime(self):
        now = datetime.now()
        self._logger.info("Current datetime: %s", now)
        return now

Important

Only works with the native Python logging module. Other libraries, such as loguru, do not support lazy calls.

For loguru, see Lazy evaluation of expensive functions:

logger.opt(lazy=True).debug("If sink level <= DEBUG: {x}", x=lambda: expensive_function(2**64))