# Lazy log formatter
Pre-commit hook to automatically detect and convert f-strings in Python code to
[printf-style](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting) 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`:
```yaml
- repo: https://github.com/dmar1n/lazy-log-formatter
rev: 0.7.0
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:
```sh
python -m src.cli
```
Check all Python files in two directories:
```sh
python -m src.cli src/ tests/
```
Fix issues in all Python files in a directory:
```sh
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:
```python
# Before
logger.info(f'Hello {name}')
# After
logger.info('Hello %s', name)
```
```python
# Before
logger.info(f'Hello {name} {surname}')
# After
logger.info('Hello %s %s', name, surname)
```
### Example in a Python class
```python
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
```
```bash
python src\cli.py tests\data
```
The output will be:
```text
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:
```python
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](https://loguru.readthedocs.io/en/stable/overview.html#lazy-evaluation-of-expensive-functions):
```python
logger.opt(lazy=True).debug("If sink level <= DEBUG: {x}", x=lambda: expensive_function(2**64))
```
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