oaknut-dfs 12.8.2

Python library for handling Acorn DFS disc images (SSD/DSD format)

oaknut-dfs

A Python library for reading, writing, and creating Acorn DFS floppy disc images, as used by the BBC Micro.

With oaknut-dfs you can open DFS floppy images (SSD/DSD) to browse the catalogue, read and write files, inspect metadata, and create new formatted discs — all from Python, with a pathlib-inspired API.

Looking for ADFS? The hierarchical Advanced Disc Filing System lives in the sibling oaknut-adfs package (from oaknut.adfs import ADFS). DFS and ADFS are independent filing systems and independent packages. For a unified command-line tool across DFS, ADFS, AFS, ROMFS and ZIP, see oaknut-disc.

Part of the oaknut monorepo.

Supported formats

• Acorn DFS — 40-track and 80-track, single-sided (SSD) and double-sided (DSD)
• Watford DFS — extended catalogue supporting up to 62 files
• DSD interleaving — both interleaved and sequential double-sided layouts

Acorn load/exec addresses, the lock bit, and the BBC Micro character set (the acorn text codec, £, ¦) are handled through the shared oaknut-file metadata layer.

Installation

uv add oaknut-dfs      # or: pip install oaknut-dfs

oaknut-dfs is a standard Python package installable with any package manager; the examples use uv.

Usage

Opening and reading files

The disc format is auto-detected from the file extension and size; pass a format explicitly only to override detection.

from oaknut.dfs import DFS

with DFS.from_file("Zalaga.ssd") as dfs:
    print(dfs.title)   # 'ZALAG-L'

    # Navigate with a pathlib-inspired API.
    for entry in dfs.root / "$":
        s = entry.stat()
        print(f"{entry.name:10s}  {s.length:6d}  load={s.load_address:08X}")

    # Read file data.
    data = (dfs.root / "$" / "ZALAGA").read_bytes()

Creating a new disc

from oaknut.dfs import DFS, ACORN_DFS_80T_SINGLE_SIDED

with DFS.create_file("demo.ssd", ACORN_DFS_80T_SINGLE_SIDED, title="DEMO") as dfs:
    (dfs.root / "$.HELLO").write_bytes(b"Hello, World!", load_address=0x1900)
    (dfs.root / "$.README").write_bytes(b"oaknut-dfs demo disc")

Double-sided discs (DSD)

A DSD image holds two independent sides, each with its own catalogue — mirroring the BBC Micro, where the sides were accessed as separate drives (*DRIVE 0 and *DRIVE 2). Select a side with the side= argument.

from oaknut.dfs import DFS

with DFS.from_file("game.dsd") as side0:
    print(side0.title)

with DFS.from_file("game.dsd", side=1) as side2:
    print(side2.title)

Walking the disc

DFS directories ($, A–Z) appear as children of a virtual root:

with DFS.from_file("disc.ssd") as dfs:
    for dirpath, dirnames, filenames in dfs.root.walk():
        for name in filenames:
            print(dirpath / name)

Development

The package is developed in the oaknut workspace. From the repository root:

uv sync                                 # install all workspace members editable
uv run pytest packages/oaknut-dfs/tests # this package's tests
uv run ruff check                       # lint

Architecture

A layered design, dependencies flowing strictly downward (every module imports only from the layer below):

DFS (dfs.py)                       user-facing DFS / DFSPath / DFSStat
  ↓
CataloguedSurface (catalogued_surface.py)
  ↓
Catalogue ABC (catalogue.py)   ←   AcornDFSCatalogue / WatfordDFSCatalogue
  ↓
Surface / SectorsView          (from oaknut-discimage)

• dfs.py — user-facing DFS, DFSPath, DFSStat; methods mirror the DFS star commands (load, save, delete, rename, lock, …).
• catalogue.py — the catalogue ABC (Catalogue, FileEntry, DiscInfo): 31-file cap, single-character directories, 7-char names.
• acorn_dfs_catalogue.py / watford_dfs_catalogue.py — the Acorn (sectors 0–1, 31 files) and Watford (sectors 0–3, 62 files) catalogues.
• catalogued_surface.py — pairs a Surface with a Catalogue.
• formats.py — DFS and Watford disc-format constants.

Sector-level access (Surface, SectorsView, UnifiedDisc) lives in oaknut-discimage; metadata and the acorn codec in oaknut-file; BBC BASIC (de)tokenisation (for DFSPath.read_basic / write_basic) in oaknut-basic.

References

• Acorn DFS disc format — BeebWiki specification for the catalogue layout.
• Disc Filing System — Wikipedia overview of DFS and its variants.
• DiscImageManager — Gerald Holdsworth's reference for DFS and other Acorn formats.
• INF file format — the .inf sidecar metadata format.

License

MIT — see LICENSE.