logfmter

library0.0.12pypypi✓ verified 86d ago

logfmter is a Python package that enables logfmt-formatted logging using the standard `logging` module without requiring changes to existing log calls. It aims to provide human and machine-readable logs, adhering to best practices like those recommended by Splunk. The current version is 0.0.12, and new releases are typically made for bug fixes, Python version support, and minor feature enhancements.

observability

pip install logfmter

github ↗package ↗

INSTALL

IMPORT

SIG · LOGFMTER

logfmter

observabilitypythonv0.0.12

Install

1.6s avg

Import

27ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v0.0.12 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.920 runs

installs and imports cleanly · install 0.0s · import 0.028s · 17.8MB

glibc

py 3.10–3.920 runs

installs and imports cleanly · install 1.6s · import 0.027s · 18MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

Logfmter

✓ from logfmter import Logfmter

This quickstart demonstrates how to integrate `logfmter` with the standard Python `logging` module using `basicConfig`. It sets up a `StreamHandler` to output logfmt-formatted messages to the console, including `extra` dictionary parameters which `logfmter` automatically flattens into key-value pairs. It also shows logging a dictionary as the main message.

import logging import os from logfmter import Logfmter # Configure a basic StreamHandler with Logfmter handler = logging.StreamHandler() handler.setFormatter(Logfmter()) # Basic configuration to use the Logfmter handler logging.basicConfig(handlers=[handler], level=os.environ.get('LOG_LEVEL', 'INFO')) # Example logs logging.info("Application started", env=os.environ.get('ENV', 'development')) logging.warning("User login failed", user_id=123, ip_address="192.168.1.1", extra={"attempts": 3}) logging.error("An unexpected error occurred", error_code="E1001") # Logging a dictionary directly as a message (keys will be flattened) logging.info({"event": "user_data_processed", "status": "success", "records": 100})

Debug

Known issues

breakingPython 3.9 support was dropped in `logfmter` v0.0.12. Users on Python 3.9 or older must pin their dependency to `logfmter<0.0.12`.

fix

Upgrade Python to 3.10 or newer, or pin `logfmter` dependency to `<0.0.12`.

affects: >=0.0.12

breakingStarting from v0.0.4, newline characters (`\n`) in all logged values are explicitly escaped to ensure single-line output per log record. If your application previously relied on generating multi-line log statements by embedding newlines, this behavior will change, and `\n` will appear literally in the output.

fix

Adjust logging messages to conform to the single-line logfmt standard. Avoid embedding newline characters or adapt your log parsing to handle escaped newlines.

affects: >=0.0.4

breakingIn v0.0.10, proper escaping of backslashes was introduced to fix issues with log consumption by third-party tools. This is a fix, but it might alter the literal string representation of backslashes in your log output if previous versions had different (and potentially incorrect) behavior.

fix

Review log parsing tools to ensure they correctly interpret properly escaped backslashes. No code change is typically needed unless relying on the prior incorrect escaping behavior.

affects: >=0.0.10

gotchaWhen using `logging.config.dictConfig` to configure logging, the `disable_existing_loggers` parameter is `True` by default. This can inadvertently disable loggers from third-party modules that were configured before `dictConfig` is called, leading to missing log output from those libraries.

fix

If you need existing loggers (e.g., from third-party libraries) to continue logging, explicitly set `"disable_existing_loggers": false` within your `dictConfig` dictionary.

affects: All

gotcha`logfmter` does not officially support configuration via `logging.config.fileConfig`. This is due to `fileConfig`'s limitation in supporting custom formatter initialization, which `logfmter` relies on.

fix

Use `logging.basicConfig` for simple setups or `logging.config.dictConfig` for more complex logging configurations.

affects: All

Errors

Common errors & fixes

Logs are not appearing in logfmt format / Not seeing any logfmter output.

`Logfmter` is not correctly applied to a `logging.Handler`, or the handler is not attached to the logger. When using `dictConfig`, `disable_existing_loggers` might be `True` by default, disabling other loggers.

fix

Ensure a `Logfmter` instance is set as the formatter for at least one `StreamHandler` or `FileHandler`, and that handler is added to the relevant logger (or root logger) using `basicConfig` or `dictConfig`. If using `dictConfig`, explicitly set `"disable_existing_loggers": false` if you need existing loggers to continue logging.

Logs show \n characters literally instead of creating newlines.

Starting from `logfmter` v0.0.4, newline characters are explicitly escaped in all logged values to ensure single-line output. This is the intended behavior.

fix

This is the designed behavior since v0.0.4. If multi-line log statements are desired (which goes against the logfmt philosophy), either downgrade `logfmter` to a version prior to 0.0.4 (not recommended, as it fixes a bug) or adjust logging to avoid embedding newlines.

ModuleNotFoundError: No module named 'logfmter'

The `logfmter` package is not installed in the current Python environment.

fix

Install the package using pip: `pip install logfmter`.

AttributeError: 'Logfmter' object has no attribute 'formatTime'

Attempting to customize date format using `formatter.datefmt` directly on the `Logfmter` instance instead of passing `datefmt` during initialization.

fix

Pass the `datefmt` parameter directly to the `Logfmter` constructor, e.g., `Logfmter(datefmt="%Y-%m-%d %H:%M:%S")`.

Upgrade

Version history

0.0.12latest on PyPI · released Mar 11, 2026

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Dependencies

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Agent activity

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Resources

githubhttps://github.com/josheppinette/python-logfmter ↗

packagehttps://pypi.org/project/logfmter/ ↗