Quick reference for symbols, notation, and abbreviations the book uses. Concept definitions live in the glossary; this page covers the shorthand only.
| Symbol | Meaning |
|---|
| §N | Section number — e.g., §5 refers to section 5. |
| → | Leads to / becomes / transitions to. Appears in section titles (e.g., §29 “10K → 1M”) and prose. |
[!NOTE] / [!TIP] / [!WARNING] | Callout box — content the reader should pay particular attention to. |
| Form | Meaning |
|---|
monospace | Code: types, variable names, function names, file paths. |
| italic | First definition of a term, or emphasis. |
| bold | A term being highlighted as load-bearing in the current paragraph. |
# anti-pattern: bad! | A code comment that flags the snippet as something the chapter is arguing against. The label travels with the code if a reader copy-pastes. |
| Variable | Meaning |
|---|
i, j | Index into a column. i is the index of the row currently under discussion. |
t or tick | Tick number — the simulator’s step counter. |
id | Stable entity identifier (a small unsigned integer; usually np.uint32). |
gen | Generation counter, paired with a slot index to detect stale references (§10). |
pos_x, pos_y | Position columns of a creature (np.float32). |
vel_x, vel_y | Velocity columns of a creature (np.float32). |
to_remove, to_insert | Buffers of pending mutations applied at end-of-tick (§22). |
n_active | Length of the live prefix of a fixed-capacity column (§21, §24). |
This book uses numpy’s typed dtypes for hot data. The mapping the reader will see most often:
| Python | numpy | size | range |
|---|
int (CPython, ≤ 2³⁰) | — | 28 bytes | unbounded |
| — | np.int8 | 1 byte | -128 to 127 |
| — | np.uint8 | 1 byte | 0 to 255 |
| — | np.int32 | 4 bytes | ±2¹ |
| — | np.uint32 | 4 bytes | 0 to 2³² |
| — | np.int64 | 8 bytes | ±2⁶³ |
float (CPython) | np.float64 | 8 bytes (CPython has 24-byte object overhead) | ~15 decimal digits |
| — | np.float32 | 4 bytes | ~7 decimal digits |
| — | np.bool_ | 1 byte (in arrays) | True / False |
| Form | Convention |
|---|
Plain triple-backtick python | A snippet to read; not necessarily complete. |
Snippet with # anti-pattern: bad! first line | A snippet shown as the wrong way; the chapter is about the right way. |
uv run code/measurement/<file>.py | A measurement exhibit the reader can run on their machine. The numbers in the chapter were measured the same way. |