Python exception gotchas run live - raise from and from None, return in finally swallowing errors, bare raise, deleted except variable

Fix Python datetime bugs - naive vs aware, UTC storage, DST gaps and folds, fromisoformat with Z, timestamps

Fix Python shared-state bugs - mutable default arguments, dataclass default_factory, class attribute sharing, shallow vs deep copy

Python file I/O - explicit encoding, UnicodeDecodeError, newline translation, utf-8-sig for BOM CSVs, mkdir exist_ok, os.replace atomic writes

Fix Python JSONDecodeError Expecting value - print status and body, HTML and empty responses, BOM, NDJSON, truncated bodies, retry rules

Fix Python ImportError - circular imports, local file shadowing stdlib, ModuleNotFoundError, python -m for packages

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

Profile slow Python - cProfile ranking, timeit min-of-N, list vs set membership measured, join vs +=, tracemalloc and generators

Python packaging basics - pyproject.toml, src layout, pip install -e, console_scripts entry point, packages.find where error

Validate JSON with Python jsonschema - iter_errors paths, required, additionalProperties, format checker, bool vs integer

Make Python requests reliable - connect and read timeouts, Session with urllib3 Retry, safe POST retries, raise_for_status and SSL errors

Python regex cookbook - findall group surprises, named groups, sub callables, lookarounds, greedy vs lazy, $ vs end anchors

Python random reproducibility - random.seed and private Random instances, shuffle returns None, sample vs choices, secrets for tokens

Python sorting gotchas - numeric strings, key=int, case and accent order, stable multi-key sorts, None TypeError, NaN breaking order

Use Python requests safely - always set timeout, raise_for_status, catch RequestException, reuse Session, check JSON content type

Use Python sqlite3 safely - ? parameter binding vs injection, implicit transactions, with conn commits but never closes, thread rule

Python concurrency - ThreadPoolExecutor vs ProcessPoolExecutor measured: CPU work slower with threads, I/O faster, lost exceptions

Run commands safely in Python - list args vs shell=True injection, check, timeouts, pipe exit codes, output

Debug poor RAG answers - check the index, retrieval hit rate, hybrid search, reranking, chunk size and context packing

Fix Redis connection refused, auth errors, max clients and timeouts - bind and protected mode, slowlog, big keys, fork stalls and client settings