structlog: Structured Logging in Python

Release v0.1.0 (Installation).

structlog makes structured logging in Python easy by augmenting your existing logger. It’s licensed under the permissive Apache License, version 2, available from PyPI, and the source code can be found on GitHub. The full documentation is on Read the Docs.

structlog targets Python 2.6, 2.7, 3.2, and 3.3 as well as PyPy with no additional dependencies for core functionality.

Why You Want Structured Logging

I believe the widespread use of format strings in logging is based on two presumptions:

  • The first level consumer of a log message is a human.
  • The programer knows what information is needed to debug an issue.

I believe these presumptions are no longer correct in server side software.

Paul Querna

Structured logging means that you don’t write hard-to-parse and hard-to-keep-consistent prose in your logs but that you log events that happen in a context instead.

Why You Want to Use structlog

Because it’s easy and you don’t have to replace your underlying logger – you just add structure to your log entries and format them to strings before they hit your real loggers.

structlog supports you with building your context as you go (e.g. if a user logs in, you bind their user name to your current logger) and log events when they happen (i.e. the user does something log-worthy):

>>> log = log.bind(user='anonymous', some_key=23)
>>> log = log.bind(user='hynek', source='http', another_key=42)
>>> log.info('user.logged_in', happy=True)
some_key=23 user='hynek' source='http' another_key=42 happy=True event='user.logged_in'

This ability to bind key/values pairs to a logger frees you from using conditionals, closures, or boilerplate methods to log out all relevant data.

Additionally, structlog offers you a flexible way to filter and modify your log entries using so called processors before the entry is passed to your real logger. The possibilities include logging in JSON, adding arbitrary meta data like timestamps, counting events as metrics, or dropping log entries caused by your monitoring system.

Why You Can Start Using structlog TODAY

  • You can use both your bare logger and as well as the same logger wrapped by structlog at the same time. structlog avoids monkeypatching so a peaceful co-existence between various loggers is unproblematic.
  • Events are free-form and interpreted as strings by default. Therefore the transition from traditional to structured logging is seamless most of the time. Just start wrapping your logger of choice and bind values later.
  • If you don’t like the idea of keeping the context within a local logger instance like in the example above, structlog offers transparent thread local storage for your context.

Intrigued? Get started now or have a look at more realistic examples and be completely convinced!

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