Detect unused loggers

[adamchainz]

Description

Sometimes modules are copy-pasta'd to create new ones, leading to the getLogger() preamble being duplicated but not used:

import logging
logger = logging.getLogger(__name__)  # never used

These unused loggers don’t take long to construct, about 1µs, but they do live forever in the logging tree (seen with logging.Logger.manager.loggerDict), wasting memory and potentially hampering efforts to debug logging.

Let’s detect and flag module-level loggers that aren’t used anywhere in their file.

(I’ve found such cases before with this regular expression: (?s)^logger = (?!.*?logger.*$))