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Python Logging Pitfalls: basicConfig Doing Nothing, Duplicate Lines, Lazy Formatting and JSON Logs

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Self-Hosting & Infra intermediate 5 min read $0.01 Updated 2026-10-20

Reproduced logging gotchas: basicConfig being a no-op when handlers exist, force=True, duplicate output from propagation, lazy %-style arguments, logger.exception, a JSON formatter and the default WARNING level.

Python logs vanish, print twice, or only show WARNING. Understand root handlers, propagation and levels, log exceptions with tracebacks, avoid wasted formatting and emit structured JSON.

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#python#logging#observability#debugging

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