yazm-py

Yet Another Z-Machine in Python — an interpreter for Infocom interactive fiction games.

Currently targets version 3 story files (.z3), such as the original Zork trilogy, Hitchhiker's Guide, and other classic Infocom titles.

Features

• Fetch-decode-execute VM for Z-machine v3 bytecode
• Full object system with tree traversal (parent/child/sibling)
• ZSCII text decoding with alphabet tables, abbreviations, and Unicode extensions
• Dictionary tokenization and input parsing
• Terminal UI with ANSI status bar and optional object highlighting
• Plain output mode (--plain) for clean piped/diffable output
• Interactive debugger with commands like $tree, $dict, $room, $find
• Pure Python 3.12+ with no runtime dependencies

Installation

Requires uv:

uv sync

Usage

# Run a game
yazm minizork.z3

# Disable object name highlighting
yazm --no-highlight lurkinghorror.z3

# Plain mode (no ANSI codes, suitable for piping)
yazm --plain czech.z3

# Run directly without installing
python -m yazm.main minizork.z3

Development

# Run all tests
pytest

# Run a single test file
pytest tests/test_zdata.py

# Lint and format
ruff check src/ tests/
ruff format src/ tests/

# Type check
uvx ty check

Architecture

The interpreter follows a fetch-decode-execute VM pattern:

File	Role
zmachine.py	Core ZMachine class: memory, object system, instruction loop, dictionary/tokenization
zinstruction.py	Decodes variable-length bytecode (LONG, SHORT, VAR, EXT forms) into Instruction dataclasses
ops.py	~50 opcode handlers dispatched via DISPATCH_TABLE (control flow, arithmetic, objects, I/O, etc.)
zdata.py	ZData(bytearray) with big-endian u8/u16 reads/writes and sequential Reader/Writer helpers
zheader.py	Parses the 64-byte story file header (version, memory layout, flags)
frame.py	Call stack Frame: resume address, local variables, evaluation stack, argument count
zscii.py	ZSCII text encoding: 5-bit packed characters, 3 alphabet tables, abbreviation expansion
zui_std.py	Terminal UI: ANSI status bar, styled output, plain mode
zdebug.py	Interactive debugger ($tree, $dict, $room, $find, etc.)
enums.py	Opcode IntEnum (~100 opcodes), operand type enums, opcode name mappings
options.py	Options dataclass for runtime config (save dir, RNG seed, highlighting)