Plasmite Python Bindings (v0)

These bindings wrap the libplasmite C ABI via ctypes.

Installation

Published wheels bundle native assets under plasmite/_native/ on the platforms where wheels are currently shipped:

• libplasmite.(dylib|so) for ctypes loading
• plasmite CLI binary (invoked via Python console script entrypoint)

Current packaged-wheel targets:

• macOS: x86_64, arm64
• Windows: x86_64

Linux currently falls back to source distribution, so runtime use there should come from a system SDK install (for example Homebrew or a GitHub release tarball) unless/until Linux wheels are added.

Using uv (recommended)

uv tool install plasmite

For project dependencies in a uv-managed workspace:

uv add plasmite

Runtime load order is:

1. PLASMITE_LIB_DIR override (development escape hatch)
2. Bundled plasmite/_native/libplasmite.(dylib|so) absolute path
3. System linker fallback (plasmite / libplasmite)

For development/testing from this repo, see Install & Test below.

Build Requirements

• Python 3.10+
• libplasmite built from this repo (cargo build -p plasmite) for local development

Install & Test

From the repo root:

cargo build -p plasmite

Canonical repo-root command:

just bindings-python-test

Equivalent manual commands (from bindings/python):

uv venv
source .venv/bin/activate
PLASMITE_LIB_DIR="$(pwd)/../../target/debug" uv pip install -e .
PLASMITE_LIB_DIR="$(pwd)/../../target/debug" PLASMITE_BIN="$(pwd)/../../target/debug/plasmite" python3 -m unittest discover -s tests

Build a wheel with bundled native assets from a specific SDK directory:

PLASMITE_SDK_DIR=/path/to/sdk python -m build

Conformance runner (manifest parity with Rust/Go/Node):

cargo build -p plasmite
cd bindings/python
PLASMITE_LIB_DIR="$(pwd)/../../target/debug" \
PLASMITE_BIN="$(pwd)/../../target/debug/plasmite" \
python3 cmd/plasmite_conformance.py ../../conformance/sample-v0.json

Usage

from plasmite import Client, Durability, NotFoundError

with Client("./data") as client:
    with client.pool("docs", 64 * 1024 * 1024) as pool:
        msg = pool.append({"kind": "note", "text": "hi"}, ["note"], Durability.FAST)
        print(msg.seq, msg.tags, msg.data["text"])

        fetched = pool.get(msg.seq)
        print(fetched.data["text"])

        for item in pool.tail(tags=["note"], max_messages=1, timeout_ms=100):
            print(item.seq, item.tags, item.data)

    try:
        client.open_pool("missing")
    except NotFoundError:
        print("pool not found")

Pool.append(...), Pool.get(...), Pool.tail(...), and Pool.replay(...) return typed Message values by default.

Use append_json(...) / get_json(...) only when you explicitly need raw wire bytes.

Pool.tail(..., tags=[...]) uses exact tag matching and composes with other filters using AND semantics.

Pools have bounded retention. A tail normally resumes at the next retained message if writes overtake it. Set error_on_gap=True when the consumer must distinguish that loss from an ordinary lack of matching messages:

from plasmite import RetentionGapError

try:
    for item in pool.tail(since_seq=last_seq + 1, error_on_gap=True):
        process(item)
except RetentionGapError as err:
    print(f"rebuild required; first missing sequence: {err.seq}")

Error behavior

• Invalid local arguments raise ValueError / TypeError.
• ABI/runtime failures raise typed subclasses of PlasmiteError (NotFoundError, AlreadyExistsError, BusyError, PermissionDeniedError, CorruptError, IoError, UsageError, InternalError, RetentionGapError).
• All PlasmiteError values expose kind, path, seq, and offset when present.

Troubleshooting

• Missing pool directory: pool creation creates parent directories automatically. If you call open_pool(...) on a missing pool, catch NotFoundError or use client.pool(...) to create-or-open.
• Permission denied: choose a writable pool directory (Client("/path/to/pools")) and verify directory permissions/ownership. Errors include err.path when available.

Threads and handle ownership

The Python wrapper serializes native operations and close() on each Client, Pool, Stream, and Lite3Stream instance. You can share an instance between threads without racing its native handle or freeing it during a call. Independent handles can operate concurrently. Message values are owned snapshots and can outlive the pool.

Each opened stream owns an independent handle. tail() and replay() release handle locks between reads, including while yielding messages or sleeping for replay timing. Consume each generator from one thread at a time.

close() waits for an active native call to finish; it does not interrupt a blocking stream read. Pass a finite timeout_ms when opening a stream if another thread needs to close it within a bounded wait. A stream without a timeout can keep close() waiting indefinitely.