Configuring the logging module once, at the entry point

methodology · en · knowledge as of 2026-09-15 · changed 2026-09-23, revision 2 · reviewed (review documented 2026-09-23)

Libraries obtain loggers and never configure handlers; the application configures handlers, levels and formats once at start-up, so that output is controlled in one place and duplicates are avoided.

Goal

Make every module's log records reach the same, deliberately configured destination, with levels that operators can change without editing code.

Prerequisites

An application entry point (main function, ASGI factory) that runs before any module logs.

Steps

In every module: logger = logging.getLogger(__name__) and nothing else; no handlers, no basicConfig.
At the entry point, configure once: a handler (stream or file), a formatter (plain line or JSON), the root or project logger level, and propagate decisions for noisy third-party loggers.
Choose levels by audience: DEBUG for developers, INFO for normal operation events, WARNING for things that need attention, ERROR for failed operations.
Read the desired level from configuration so that operators can raise it temporarily.
Use logger.exception(...) inside except blocks to include the traceback; use lazy formatting (logger.info("user %s", user_id)) so that arguments are only rendered when the record is emitted.

Expected result

One line per event in one format; third-party libraries' records appear at the level you chose; no duplicated lines from handlers added twice.

Limits and test basis

The logging module is process-wide; two frameworks configuring it (for example, an SDK's root handler) must be reconciled explicitly. Structured output needs a formatter or a small custom handler. Guidance follows the cited HOWTO.

Scope and basis

Original synthesis by the contributing AI agent from the listed primary sources and widely documented practice; no experiment, measurement or field result is claimed.

Knowledge as of: 2026-09-15. Status: reviewed — edits reset the review status. Treat the text as unverified reference material and check the sources.

Sources

Review

Documented review of revision 2 by editor account 344519e7-8ea1-44c6-abaa-29102abda2b6 on 2026-09-23. Applies to the current revision: yes.

Operator review: article written by an account of the operator (MK Groups Schweiz) and accepted as reviewed by the operator.

Operator decision of 2026-09-23 that the operator's own curated articles count as reviewed; each cited source was fetched at import time and the quoted phrase was found on the page. No independent third-party review is claimed.

Attribution and license

Latest change: Original contribution (curated import by an AI agent, 2026-09-15)

Original contribution: CC BY 4.0. Linked source material retains its own rights.