log_setup

Stdlib, sync, zero-dependency logging setup an application calls once at its entry point: a live run.log, rotation (daily / size / on-start), gzip of rolled files, retention, console output, and a consistent time | module | level | message format.

It configures logging (handlers, rotation, format) — which reusable libraries here must never do. That's fine because log_setup is the application's entry-point setup, not library-internal config. Libraries still only logging.getLogger(__name__) and emit; their records flow into the handlers log_setup wired.

Install

log_setup @ git+ssh://git@git.rethinkstudios.io/rethink-public/log_setup.git@v0.2.0

No dependencies — stdlib only.

Quick start

import logging
from log_setup import setup_logging

setup_logging(name="run", level="INFO")     # daily rotation, logs/ dir, gzip (file only)

log = logging.getLogger(__name__)
log.info("started")                          # -> ./run.log  (add console=True for stdout too)

Call it once, at the app's entry point — before the rest of the app runs. Every module (yours and the libraries you import) then just does logging.getLogger(__name__) and emits; the records land in the configured root.

What you get

• Live file at a stable path: ./run.log — always tail -f run.log, no dated name to chase. Rolled/compressed copies go into log_dir (default logs/).
• Format: 2026-06-27 19:55:05 | module.name | INFO | message. %(name)s is the getLogger name each module used, so you see which lib/module logged.
• Rotation (rotate=):
  • "daily" (default) — rolls at midnight, dated name into log_dir, keeps backup_count days.
  • "size" — rolls at max_bytes, numbered backups in log_dir.
  • "on_start" — on startup, moves an existing run.log into log_dir (run.<timestamp>.log[.gz]) and starts fresh; prunes to backup_count.
  • None — single file, no rotation.
• compress=True (default) gzips each rolled file (run.log.2026-06-27.gz).
• Retention = backup_count (default 14) for every mode.
• console=True (off by default) also logs to stdout in the same format — opt in when you want live terminal output alongside the file.

Output format (output=)

Two formats, two needs. Default is "text"; the live-file name is the same either way (run.log, never auto-renamed), so a service can switch text↔json without breaking the Promtail glob, bind-mount path, or your tail command.

• output="text" (default) — human-readable 2026-06-27 19:55:05 | module.name | INFO | message, local time. The single-machine tail -f path. fmt/datefmt override it. Unchanged from v0.1.x.
• output="json" — structured one JSON object per line (JSON Lines) for the Grafana/Loki pipeline (Promtail → Loki → Grafana); Loki parses JSON fields into labels natively, no regex.

setup_logging(name="run", output="json")
logging.getLogger("bot.core").info("ready", extra={"monitor": "heartbeat"})
# -> {"time": "2026-06-28T14:03:11Z", "level": "INFO", "module": "bot.core",
#     "message": "ready", "monitor": "heartbeat"}

• Fields: time, level, module, message always; any extra={...} keys land as top-level fields (stamp monitor/service/request-id for Loki labels — the lib stays domain-agnostic); error records carry the traceback in exc_info (never dropped).
• Time is UTC ISO-8601 with a Z (2026-06-28T14:03:11Z), not local. json is the aggregation path — logs from many servers/containers sort unambiguously only in UTC; Grafana converts to local for display. (Text mode stays local — that's a human on one box.)
• Both file and console use the chosen format. fmt/datefmt apply to text only (json builds fields, not a format string). An unknown output falls back to text + warns, never crashes. Zero new deps — stdlib json only.

Signature

setup_logging(
    name="run",               # base -> run.log (the live file at cwd)
    log_dir="logs",           # rotated/compressed copies live here (created if absent)
    level="INFO",             # root level (str name or logging constant)
    rotate="daily",           # "daily" | "size" | "on_start" | None
    backup_count=14,          # rotated files to keep (older auto-deleted)
    max_bytes=10_000_000,     # only for rotate="size"
    compress=True,            # gzip rolled files
    console=False,            # also log to stdout (off by default; opt in)
    queue=False,              # route through a background QueueListener (async-friendly)
    output="text",            # "text" (human, local time) | "json" (structured, UTC)
    fmt=None,                 # override the text format string (text mode only)
    datefmt=None,             # override the text date format (text mode only)
) -> logging.Logger           # returns the configured root logger

Async-friendly (queue=True)

For async-heavy apps, queue=True routes records through a stdlib QueueHandler to a background QueueListener that owns the file/console handlers, so the event loop never blocks on file I/O. The API stays sync (log.info() as usual); the queue is internal. The listener is stopped (and flushed) cleanly at process exit, so no records are lost.

setup_logging(name="run", queue=True)

Safety

• Idempotent: calling setup_logging again clears only the handlers it added (no duplicate lines) and leaves handlers your app added itself alone.
• Never crashes the app over logging: if log_dir isn't writable, it falls back to console-only with a warning instead of raising.

Scope — what this is NOT

log_setup produces clean, rotating, compressed, retention-managed, consistently formatted files. It does not ship logs anywhere — no Loki/ELK/syslog/network handlers. Getting files to a backend is a separate concern (e.g. Promtail tails run.log → Loki → Grafana panels + alerting). Keeping shipping out means the log backend can change without touching any app, and the consistent format here is what makes downstream parsing and alerting easy.

Structured/JSON output is in as of v0.2.0 (output="json") — text and json only. Still deliberately out: logfmt or other formats, a format DSL, per-handler formats, color formatting, per-logger filters, remote handlers.

Versioning

Tagged vX.Y.Z. Pin the tag.