Selected every rule the Python linter has as an error, working through 1,815 findings to reach zero, with each of the few exemptions carrying a written reason and two of them backed by a checker instead of a comment.

Situation. Most projects pick a comfortable subset of their linter’s rules, and the subset is chosen by whichever rules were quiet on the day it was configured. That makes the configuration a record of the code’s existing habits rather than a standard the code is held to, and every rule left off is a class of defect nobody will ever be told about.

Task. The default had to be inverted — every rule the tool implements enabled as an error — and the resulting backlog worked to zero rather than negotiated down by turning rules back off.

Action. Selecting the complete rule set produced 1,815 findings on first run. They were worked through by category rather than by file, because the categories tell you something: unused arguments and shadowed builtins are noise, but the security category, the mutable‑default category and the exception‑handling category each pointed at real behaviour. Genuine incompatibilities exist — a formatter and a linter can disagree about the same line, and a few rules contradict the project’s own deliberate choices — and each of the small number of exemptions carries a written reason at the point of exemption saying what the rule wanted and why this code does otherwise. Two of them go further and are backed by a check rather than a comment, so the exemption cannot quietly widen: the rule is off, and a test asserts the specific property the rule would have enforced. Type checking runs in strict mode alongside it, which is a separate and harder standard, and it is the one that caught defects the linter could not see because they are about what a value is rather than how it is written.

Result. The linter runs at full strength with zero findings, and every deviation is documented at the line where it is taken. The cost is real and worth naming: the strictest setting produces findings that are genuinely not worth acting on, and someone has to make that judgement 1,815 times rather than once.