09_The_Standard_Library — the modules whose names promise more than they do

Level: 201 → 301 · for Python programmers

A module's name is a promise, and the promises the standard library makes are narrower than they sound. json writes JSON, which has six types and none of them is a tuple. A Path is not a string. An Enum member is not its value. A defaultdict creates a key when you only meant to look. lru_cache keys on the call as written. logging is a tree, and a record climbs it. Each page here is one such name and the gap between what it says and what it does, measured.

#	Lesson	The question it answers	Status
1	json is not Python	Why did my tuple come back a list, my int key a str, and my Polish text as Ł — and why did none of that raise?	written
2	A Path is not a string	Why is path + '.bak' a TypeError — and which Path methods touch the disk?	stub
3	An Enum member is not its value	Why is Color.RED == 1 False — and why did two members turn out to be one?	stub
4	defaultdict creates on read	Why did my dict grow during a loop that only read from it?	stub
5	lru_cache keys on the call	Why are f(1) and f(x=1) two cache entries — and why did my objects stop being garbage-collected?	stub
6	logging is a tree	Why is every line printed twice — and why did basicConfig() do nothing?	stub

Where this sits relative to the other libraries

The modules other libraries own are not here. re belongs to the regex library ↗, codecs to the encodings library through chapter 1's The codecs registry, and threading, asyncio, multiprocessing and concurrent.futures to the concurrency library ↗. For page 1 the Rust library's data chapter ↗ is the typed alternative, where the type is the schema and a round trip is an identity.