python-cookbook

# Stas' Python Cookbook > Distilled from **Stas' Python Cookbook** open book by Stas Bekman - source: https://github.com/stas00/python-cookbook (CC BY-SA 4.0). This skill is a condensed index; each section links back to the full chapter for depth, runnable snippets, and gotchas. A practical, standard-library-first reference for the Python idioms that come up again and again in real work. It leads with the *why*, shows the *how* with copy-paste snippets, and calls out the gotchas that bite in practice. Targets **Python 3.8+**; version-specific features are flagged inline. For deep single-process/tool debugging (gdb, strace, py-spy, core files, CUDA) pair this with [The Art of Debugging](https://github.com/stas00/the-art-of-debugging/blob/master/SKILL.md). ## Core principles - **Reach for the standard library first.** A third-party package is only suggested when the stdlib genuinely falls short - and it's flagged with `pip install`. - **Prefer the modern idiom.** f-strings over `%`/`.format()`, `pathlib` over `os.path`, `subprocess.run` over `os.system`, dataclasses over ad-hoc tuples, `logging` over `print` in real programs. - **Know the gotcha before it bites.** Mutable default arguments, shallow vs deep copy, pass-by-object-reference, naive vs aware datetimes, the GIL - each chapter flags the trap. - **Read the linked section before applying a recipe** - each has worked examples, caveats, and edge cases the one-liner here omits. ## Part I - Language core Full chapters: [Strings](https://github.com/stas00/python-cookbook/blob/master/content/README.md#strings-and-text) · [Formatting](https://github.com/stas00/python-cookbook/blob/master/content/README.md#string-formatting) · [Numbers](https://github.com/stas00/python-cookbook/blob/master/content/README.md#numbers-and-math) · [Regex](https://github.com/stas00/python-cookbook/blob/master/content/README.md#regular-expressions). - **Text wrangling:** case/containment/split/join/strip/replace, encoding-decoding, and a [worked text-normalization example](https://github.com/stas00/python-cookbook/blob/master/content/README.md#regular-expressions). Compare strings with a [readable diff](https://github.com/stas00/python-cookbook/blob/master/content/README.md#strings-and-text). See [Strings and Text](https://github.com/stas00/python-cookbook/blob/master/content/README.md#strings-and-text). - **Formatting:** the [format spec mini-language](https://github.com/stas00/python-cookbook/blob/master/content/README.md#string-formatting) (alignment, padding, precision, `,`/`_` grouping), [f-string tricks](https://github.com/stas00/python-cookbook/blob/master/content/README.md#string-formatting) (`=` debug, nested specs), and number/byte humanization. See [String Formatting](https://github.com/stas00/python-cookbook/blob/master/content/README.md#string-formatting). - **Numbers/math:** rounding traps, `decimal`/`fractions`, [statistics without NumPy](https://github.com/stas00/python-cookbook/blob/master/content/README.md#numbers-and-math), and special values (`nan`/`inf`). See [Numbers and Math](https://github.com/stas00/python-cookbook/blob/master/content/README.md#numbers-and-math). - **Regex:** the [core functions](https://github.com/stas00/python-cookbook/blob/master/content/README.md#regular-expressions), flags, groups/assertions, substitution with backreferences/callables, splitting, and escaping literals. See [Regular Expressions](https://github.com/stas00/python-cookbook/blob/master/content/README.md#regular-expressions). ## Part I - Data structures Full chapters: [Lists](https://github.com/stas00/python-cookbook/blob/master/content/README.md#lists) · [Tuples](https://github.com/stas00/python-cookbook/blob/master/content/README.md#tuples) · [Sets](https://github.com/stas00/python-cookbook/blob/master/content/README.md#sets) · [Dictionaries](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries) · [Comprehensions/itertools](https://github.com/stas00/python-cookbook/blob/master/content/README.md#comprehensions-iterators-and-itertools). - **Lists:** add/remove, [shallow vs deep copy](https://github.com/stas00/python-cookbook/blob/master/content/README.md#lists) (a classic bug source), slicing/splicing, searching/aggregating, chunking, and ranges. See [Lists](https://github.com/stas00/python-cookbook/blob/master/content/README.md#lists). - **Tuples & sets:** immutability and namedtuples ([Tuples](https://github.com/stas00/python-cookbook/blob/master/content/README.md#tuples)); set algebra and mutation ([Sets](https://github.com/stas00/python-cookbook/blob/master/content/README.md#sets)). - **Dictionaries:** construction/merging (`|`), [access with defaults](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries), [`defaultdict`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries), [`Counter`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries), transformations, and [dataclasses for structured records](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries). See [Dictionaries](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dictionaries). - **Comprehensions & iterators:** list/dict/set/generator forms, [the essential itertools](https://github.com/stas00/python-cookbook/blob/master/content/README.md#comprehensions-iterators-and-itertools), flatten/zip/unzip, and [generators with `yield`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#comprehensions-iterators-and-itertools) for streaming. See [Comprehensions, Iterators and itertools](https://github.com/stas00/python-cookbook/blob/master/content/README.md#comprehensions-iterators-and-itertools). ## Part I - Functions, classes, time Full chapters: [Functions](https://github.com/stas00/python-cookbook/blob/master/content/README.md#functions) · [Classes](https://github.com/stas00/python-cookbook/blob/master/content/README.md#classes-and-objects) · [Dates](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dates-and-times). - **Functions:** `*args`/`**kwargs`, the [mutable-default-argument trap](https://github.com/stas00/python-cookbook/blob/master/content/README.md#functions), [pass-by-object-reference](https://github.com/stas00/python-cookbook/blob/master/content/README.md#functions), closures, `functools` (partial/`lru_cache`/reduce), and [decorators](https://github.com/stas00/python-cookbook/blob/master/content/README.md#functions). See [Functions](https://github.com/stas00/python-cookbook/blob/master/content/README.md#functions). - **Classes:** dunder methods, inheritance, dynamic attributes/delegation, [importing a class from a string](https://github.com/stas00/python-cookbook/blob/master/content/README.md#classes-and-objects), and [context managers](https://github.com/stas00/python-cookbook/blob/master/content/README.md#classes-and-objects). See [Classes and Objects](https://github.com/stas00/python-cookbook/blob/master/content/README.md#classes-and-objects). - **Dates/times:** parsing/formatting, [always use timezone-aware datetimes](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dates-and-times), durations, and measuring elapsed time. See [Dates and Times](https://github.com/stas00/python-cookbook/blob/master/content/README.md#dates-and-times). ## Part II - Runtime & environment Full chapters: [Modules](https://github.com/stas00/python-cookbook/blob/master/content/README.md#modules-and-imports) · [Files/IO](https://github.com/stas00/python-cookbook/blob/master/content/README.md#files-paths-and-io) · [Env & args](https://github.com/stas00/python-cookbook/blob/master/content/README.md#environment-variables-and-program-arguments) · [Subprocess](https://github.com/stas00/python-cookbook/blob/master/content/README.md#subprocess-and-shell-integration). - **Modules/imports:** how [`sys.path`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#modules-and-imports) resolves imports, inspecting/reloading modules, and dynamic import. See [Modules and Imports](https://github.com/stas00/python-cookbook/blob/master/content/README.md#modules-and-imports). - **Files/paths/IO:** [`pathlib` basics](https://github.com/stas00/python-cookbook/blob/master/content/README.md#files-paths-and-io), metadata, create/move/delete, globbing, [reading/writing](https://github.com/stas00/python-cookbook/blob/master/content/README.md#files-paths-and-io), and [temp files/dirs](https://github.com/stas00/python-cookbook/blob/master/content/README.md#files-paths-and-io). See [Files, Paths and I/O](https://github.com/stas00/python-cookbook/blob/master/content/README.md#files-paths-and-io). - **Env vars & CLI:** reading [environment variables](https://github.com/stas00/python-cookbook/blob/master/content/README.md#environment-variables-and-program-arguments) safely, [`argparse`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#environment-variables-and-program-arguments), and replaying the exact command line. See [Environment Variables and Program Arguments](https://github.com/stas00/python-cookbook/blob/master/content/README.md#environment-variables-and-program-arguments). - **Subprocess:** run external commands with `subprocess.run` (capture output, check errors, avoid `shell=True` pitfalls) instead of `os.system`. See [Subprocess and Shell Integration](https://github.com/stas00/python-cookbook/blob/master/content/README.md#subprocess-and-shell-integration). ## Part II - Data, concurrency, network Full chapters: [Serialization](https://github.com/stas00/python-cookbook/blob/master/content/README.md#serialization-json-csv-pickle-xml-gzip) · [Concurrency](https://github.com/stas00/python-cookbook/blob/master/content/README.md#concurrency-processes-threads-and-the-gil) · [Networking](https://github.com/stas00/python-cookbook/blob/master/content/README.md#networking). - **Serialization:** [JSON](https://github.com/stas00/python-cookbook/blob/master/content/README.md#serialization-json-csv-pickle-xml-gzip) (custom encoders, streaming), CSV, pickle (and its security caveat), gzip, [memory-safe streaming XML](https://github.com/stas00/python-cookbook/blob/master/content/README.md#serialization-json-csv-pickle-xml-gzip), and archives. See [Serialization](https://github.com/stas00/python-cookbook/blob/master/content/README.md#serialization-json-csv-pickle-xml-gzip). - **Concurrency:** the [GIL](https://github.com/stas00/python-cookbook/blob/master/content/README.md#concurrency-processes-threads-and-the-gil) and when to use processes vs threads, process pools, the unified [`concurrent.futures`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#concurrency-processes-threads-and-the-gil) API, and background monitoring threads. See [Concurrency](https://github.com/stas00/python-cookbook/blob/master/content/README.md#concurrency-processes-threads-and-the-gil). - **Networking:** sockets/ports and [HTTP with `requests`](https://github.com/stas00/python-cookbook/blob/master/content/README.md#networking). See [Networking](https://github.com/stas00/python-cookbook/blob/master/content/README.md#networking). ## Part III - Debugging, profiling & testing Full chapters: [Logging](https://github.com/stas00/python-cookbook/blob/master/content/README.md#printing-logging-and-output-control) · [Debugging](https://github.com/stas00/python-cookbook/blob/master/content/README.md#debugging) · [Introspection](https://github.com/stas00/python-cookbook/blob/master/content/README.md#introspection-and-object-inspection) · [Profiling](https://github.com/stas00/python-cookbook/blob/master/content/README.md#profiling-cpu-and-memory) · [Exceptions](https://github.com/stas00/python-cookbook/blob/master/content/README.md#exceptions-and-error-handling) · [Testing](https://github.com/stas00/python-cookbook/blob/master/content/README.md#testing-with-pytest-and-unittest).