.tip

Jul 5, 2026 · one of the small things

pytest -x --lf when you are fixing a failure

-x stops at the first failure, and --lf only runs the tests that failed last time. Together they turn a five minute suite into a five second loop while you work on whatever's broken.

pytest -x --lf

When you think you've fixed it, --ff runs the failures first and then everything else.

pythontesting

~/tips/today — 2026-10-19

~cat tips/today

Never build an index on a live table without CONCURRENTLY

postgresqlmigrations

A plain CREATE INDEX takes a lock that blocks every write to the table for the whole build. On a big table that means minutes of outage that look like a hung app.

CREATE INDEX CONCURRENTLY orders_customer_idx ON orders (customer_id);

It's slower and can't run inside a transaction, so you'll have to tell your migration tool. If it fails halfway, it leaves an invalid index behind, so check pg_index.indisvalid and drop it before you retry.

↵ open y yesterday l ls /tips

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