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log-no-print (BTLOG002)

Added in 0.8.0 · Stable · Enabled by default (warning)

Family: logging · Standard: CES-46 · Languages: javascript, python, tsx, typescript

Directive

Importable library code logs through a logger. In Python, print(), sys.stdout.write() and sys.stderr.write() are violations. In TypeScript and JavaScript (.ts, .tsx, .js), a call to console.log, info, debug, warn, error, trace, dir or table, and process.stdout.write() or process.stderr.write(), are violations. A warning by default.

Why

These calls write unstructured text to stdout or stderr, with no level, timestamp or context, and a library that prints pollutes the output of every program that imports it. Logging lets the application decide where output goes.

Exceptions

The entry points of a command line program and the tests write there on purpose. Another entry point goes in the extend-ignores of the rule.

The rule skips:

  • __main__.py, cli.py and every file under a cli/ directory.
  • conftest.py and every file under tests/.
  • A write inside an if __name__ == "__main__": block.

TypeScript and JavaScript

The rule skips:

  • cli.* and every file under a cli/ or bin/ directory.
  • *.test.*, *.spec.* and every file under __tests__/ or tests/.
  • A write inside an if (import.meta.main) or if (require.main === module) block.

Do

Log through the house get_logger (botica refs show structured-logging):

log = get_logger(__name__)


def fetch(key):
    log.info("cache miss", key=key)

Log through the logger of the project:

export function run(): void {
  logger.info("running");
}

Don't

def fetch(key):
    print("cache miss", key)

export function run(): void {
  console.log("running");
}

Suppression

A comment on the line silences it. There are two forms: # botica: ignore[<slug>] names the rule by its slug, and # noqa: <code> -- <reason> names it by its code, with the reason after --.

print("cache miss", key)  # botica: ignore[log-no-print]
print("cache miss", key)  # noqa: BTLOG002 -- reason

One comment silences one line. It names the rule by its slug.

console.log("running"); // botica: ignore[log-no-print]

References

Discussion