fix(python): preserve pylance distribution variant

docs/src/python/python.md

@@ -17,6 +17,25 @@ The general flow of using the API is:
 pip install lancedb
 ```
 
+The core package does not require PyLance. When you need access to the underlying
+Lance dataset or GPU-accelerated indexing, add the `pylance` extra to the
+distribution you already installed.
+
+For the standard distribution:
+
+```shell
+pip install "lancedb[pylance]"
+```
+
+For the pre-Haswell compatibility distribution:
+
+```shell
+pip install "lancedb-compat[pylance]"
+```
+
+Use only the extra matching your installed distribution. Do not install both
+distributions because they share the `lancedb` namespace.
+
 The following methods describe the synchronous API client. There
 is also an [asynchronous API client](#connections-asynchronous).
 

python/README.md

@@ -8,6 +8,25 @@ A Python library for [LanceDB](https://github.com/lancedb/lancedb).
 pip install lancedb
 ```
 
+The core package does not require PyLance. When you need access to the underlying
+Lance dataset or GPU-accelerated indexing, add the `pylance` extra to the
+distribution you already installed.
+
+For the standard distribution:
+
+```bash
+pip install "lancedb[pylance]"
+```
+
+For the pre-Haswell compatibility distribution:
+
+```bash
+pip install "lancedb-compat[pylance]"
+```
+
+Use only the extra matching your installed distribution. Do not install both
+distributions because they share the `lancedb` namespace.
+
 ### 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`.

python/python/lancedb/table.py

@@ -117,6 +117,14 @@ _MODEL_BACKED_TOKENIZER_ERRORS = (
     "Failed to initialize default tokenizer",
 )
 
+_PYLANCE_INSTALL_ERROR = (
+    "The lance library is required to use this function. Install the PyLance "
+    "extra for the distribution already installed: "
+    '`pip install "lancedb[pylance]"` for `lancedb`, or '
+    '`pip install "lancedb-compat[pylance]"` for `lancedb-compat`. '
+    "Do not install both distributions because they share the `lancedb` namespace."
+)
+
 
 def _add_unique_note(exception: BaseException, note: str) -> None:
     existing_notes = getattr(exception, "__notes__", ()) or ()
@@ -2249,10 +2257,7 @@ class LanceTable(Table):
         try:
             import lance
         except ImportError:
-            raise ImportError(
-                "The lance library is required to use this function. "
-                "Please install with `pip install pylance`."
-            )
+            raise ImportError(_PYLANCE_INSTALL_ERROR)
 
         branch = self.current_branch()
         version = None if branch is not None else self.version
@@ -4757,10 +4762,7 @@ class AsyncTable:
         try:
             import lance
         except ImportError:
-            raise ImportError(
-                "The lance library is required to use this function. "
-                "Please install with `pip install pylance`."
-            )
+            raise ImportError(_PYLANCE_INSTALL_ERROR)
 
         # lance.dataset() can't open a branch directly, so open the base table
         # and check out the branch ref (a None branch resolves to main).

python/python/tests/test_import.py

@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+import subprocess
+import sys
+
+
+def test_import_lancedb_without_pylance():
+    script = """
+import sys
+
+
+class BlockLanceImports:
+    def find_spec(self, fullname, path=None, target=None):
+        if fullname == "lance" or fullname.startswith("lance."):
+            raise ModuleNotFoundError(f"blocked optional dependency: {fullname}")
+        return None
+
+
+sys.meta_path.insert(0, BlockLanceImports())
+import lancedb
+"""
+
+    result = subprocess.run(
+        [sys.executable, "-c", script],
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.returncode == 0, result.stderr

python/python/tests/test_table.py

@@ -1258,6 +1258,24 @@ def test_branch_to_lance_targets_branch(tmp_path):
     assert table.to_lance().count_rows() == 1
 
 
+def _assert_pylance_install_error(error: ImportError):
+    message = str(error)
+    assert 'pip install "lancedb[pylance]"' in message
+    assert 'pip install "lancedb-compat[pylance]"' in message
+    assert "distribution already installed" in message
+    assert "Do not install both distributions" in message
+
+
+def test_to_lance_recommends_pylance_extra(tmp_db):
+    table = tmp_db.create_table("t", [{"i": 1}])
+
+    with patch("builtins.__import__", side_effect=ImportError):
+        with pytest.raises(ImportError) as exc_info:
+            table.to_lance()
+
+    _assert_pylance_install_error(exc_info.value)
+
+
 @pytest.mark.asyncio
 async def test_async_to_lance(tmp_path):
     pytest.importorskip("lance")
@@ -1269,6 +1287,18 @@ async def test_async_to_lance(tmp_path):
     assert dataset.count_rows() == 1
 
 
+@pytest.mark.asyncio
+async def test_async_to_lance_recommends_pylance_extra(tmp_path):
+    db = await lancedb.connect_async(tmp_path)
+    table = await db.create_table("t", [{"i": 1}])
+
+    with patch("builtins.__import__", side_effect=ImportError):
+        with pytest.raises(ImportError) as exc_info:
+            await table.to_lance()
+
+    _assert_pylance_install_error(exc_info.value)
+
+
 @pytest.mark.asyncio
 async def test_async_branch_to_lance_targets_branch(tmp_path):
     pytest.importorskip("lance")