04_Python — str, bytes, and the boundary between them

Level: 101 → 201 · for Python programmers

Python draws the text/bytes line as a type boundary and refuses to cross it silently. These lessons are what you already know about str and bytes, reorganised around chapter 2 and chapter 3, plus the places the boundary is easy to get wrong: open(), the errors policy, the bytes that are not text at all, normalization, and binary formats.

#	Lesson	The question it answers	Status
1	str vs bytes	Which is which, and why will Python not concatenate them?	stub
2	Encode, decode and errors	What do the eight errors= policies each throw away, and which one can be undone?	written, 2026-09-07
3	Bytes that are not text	How does os.listdir() hand me a filename that is not UTF-8, and hand it back unchanged?	written, 2026-09-07
4	Opening a file	Why is open(path) a bet, and what is the portable call?	written, 2026-09-07
5	Normalization	Why can 'é' == 'é' be False, and what do I run before comparing?	written, 2026-09-06
6	Bytes, hex and int	How do I read a binary format by hand with four conversions?	written, 2026-09-07
7	A str in memory	Why can one emoji quadruple what a string costs, and why is len() still O(1)?	written, 2026-09-07