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## Summary - keep the existing synchronous `connect()` path unchanged - make `LanceDBConnection.__repr__` and `LanceTable.__repr__` side-effect-free - add a regression test that verifies sync reprs do not call the Python background loop ## Root cause The freeze is caused by debugger rendering, not by `connect()` itself: 1. debugpy stops at a breakpoint and suspends all Python threads. 2. The debugger renders the new `db_connection` local by calling `repr()`. 3. `LanceDBConnection.__repr__` reads `read_consistency_interval`. 4. That property calls `LOOP.run(...).result()`. 5. The `LanceDBBackgroundEventLoop` thread is suspended by the debugger, so `repr()` waits for a thread that cannot run. This explains why the symptom appears immediately after `connect()`: it is the first point where a connection object exists in locals and is automatically rendered. `LanceTable.__repr__` had the same problem because it also read the connection's consistency interval. This follows the same principle as #3411: `__repr__` must not trigger async work or I/O that a debugger assumes is lightweight. ## Evidence I reproduced the behavior with the real LanceDB classes and debugpy 1.8.21 using a DAP client: - latest `main` (`ff6ff099`): the debugger reported `allThreadsStopped: true`, and evaluating `repr(db_connection)` timed out - this branch (`5755a5ba`): the same evaluation returned `LanceDBConnection(uri='/tmp/lancedb-debug-repro')` immediately - setting `PYDEVD_UNBLOCK_THREADS_TIMEOUT=0` also allowed the original repr path to complete, independently confirming that it was waiting on a suspended thread The regression test creates a connection and table, replaces `LOOP.run` with a function that fails, and verifies that both reprs still work. ## Validation - `maturin develop --manifest-path python/Cargo.toml` - `python -m pytest python/python/tests/test_db.py::test_sync_repr_does_not_use_background_loop python/python/tests/test_table.py::test_consistency -q` (`4 passed`) - `ruff check .` - `ruff format --check python/python/lancedb/db.py python/python/lancedb/table.py python/python/tests/test_db.py python/python/tests/test_table.py` - `git diff --check` Refs #3611.
LanceDB Python SDK
A Python library for LanceDB.
Installation
pip install lancedb
Pre-Haswell x86_64 hosts: lancedb-compat
The default lancedb wheel targets x86-64-haswell (AVX2 + FMA + F16C) for full performance on modern hardware. Pre-Haswell hosts — Intel Sandy Bridge / Ivy Bridge / Westmere; AMD Bulldozer / Piledriver / Steamroller — don't have AVX2 and crash with Illegal instruction at import lancedb.
For those hosts, install the lancedb-compat package instead:
pip install lancedb-compat
Same Python API (import lancedb works as usual). The compat wheel is compiled at the x86-64-v2 baseline (Nehalem-class) and uses runtime SIMD dispatch in the embedded lance crate to pick the right kernel tier (scalar / AVX / AVX+FMA / AVX2+FMA / AVX-512) at load time, so it still goes fast on modern hardware while running cleanly on the pre-Haswell silicon. Use lance.simd_info() from Python to verify which tier was selected.
lancedb and lancedb-compat install to the same lancedb/ namespace and conflict at install time. Pick one. To switch, pip uninstall lancedb first, then pip install lancedb-compat (or vice-versa).
If you need a custom baseline (or lancedb-compat isn't yet published for your platform), build from source with the override:
RUSTFLAGS="-C target-cpu=x86-64-v2" maturin build --release
pip install ./target/wheels/lancedb-*.whl
Preview Releases
Stable releases are created about every 2 weeks. For the latest features and bug fixes, you can install the preview release. These releases receive the same level of testing as stable releases, but are not guaranteed to be available for more than 6 months after they are released. Once your application is stable, we recommend switching to stable releases.
pip install --pre --extra-index-url https://pypi.fury.io/lancedb/ lancedb
Usage
Basic Example
import lancedb
db = lancedb.connect('<PATH_TO_LANCEDB_DATASET>')
table = db.open_table('my_table')
results = table.search([0.1, 0.3]).limit(20).to_list()
print(results)
Development
See CONTRIBUTING.md for information on how to contribute to LanceDB.