Running split calculator for even-pace race planning - pace, split time and split count

Procurement reorder point calculator - safety stock, inventory position and reorder-now flag from demand and lead time

Aspect ratio calculator - reduce width and height to a ratio and orientation

Build a Python argparse CLI - subparsers, choices, count and append flags, exit code 2, why options after a subcommand fail

Read mypy errors - Optional None narrowing, return-value and arg-type mismatches, attr-defined, strict no-untyped-def, implicit Optional

NDJSON and JSON Lines in Python and jq - write, stream, skip corrupt lines, Extra data errors, NaN, ensure_ascii

Video frame count and frame interval from frame rate and duration

Never use floats for money - integer minor units or decimals, currency exponents, explicit rounding modes, cent-safe allocation and tax order

Find and fix flaky pytest tests - random order, repeat and xdist reproduction, shared state, fixture scope, time, network and async races

Pytest mocking - patch where the name is used, autospec to catch bad calls, side_effect for retries, monkeypatch, freezegun

Fix Python asyncio - never awaited coroutine, blocking the loop, gather return_exceptions, wait_for, Semaphore, cancel

Average video bitrate calculator from duration and file size - Mbps and kbps

Pytest fixtures explained - session/module/function order logged, autouse, module-scope state leak failing assert 2 == 1, --setup-show, fixture not found

Python gotchas run live - late-binding lambdas return [2, 2, 2], exhausted generators, dict mutation RuntimeError, shared nested lists

Python context managers run live - @contextmanager needs try/finally, __exit__ returning True swallows errors, suppress, ExitStack

Python collections gotchas - defaultdict read creates keys, Counter drops negative counts, deque maxlen discards, shallow dict copy shares nested

Debug Python asyncio hangs and slowdowns - blocking calls in the event loop, unawaited coroutines, lost tasks, timeouts and gather errors

Fix Python multiprocessing - PicklingError for lambdas, local function hangs Pool.map under spawn, locks not picklable, shared Value counter

Python lru_cache pitfalls - eviction demo, unhashable list TypeError, methods keep instances alive, stale values, shared mutable results

Python environment variable config - bool(false-string) trap, KeyError vs default, empty vs unset, subprocess env replace, .env parsing