fix(python): document optional pylance installation

python/README.md

@@ -8,6 +8,14 @@ A Python library for [LanceDB](https://github.com/lancedb/lancedb).
 pip install lancedb
 ```
 
+The core package does not require PyLance. Install LanceDB's optional PyLance
+dependency when you need access to the underlying Lance dataset or
+GPU-accelerated indexing:
+
+```bash
+pip install "lancedb[pylance]"
+```
+
 ### 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

@@ -2251,7 +2251,7 @@ class LanceTable(Table):
         except ImportError:
             raise ImportError(
                 "The lance library is required to use this function. "
-                "Please install with `pip install pylance`."
+                'Please install with `pip install "lancedb[pylance]"`.'
             )
 
         branch = self.current_branch()
@@ -4759,7 +4759,7 @@ class AsyncTable:
         except ImportError:
             raise ImportError(
                 "The lance library is required to use this function. "
-                "Please install with `pip install pylance`."
+                'Please install with `pip install "lancedb[pylance]"`.'
             )
 
         # lance.dataset() can't open a branch directly, so open the base table

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 +1258,14 @@ def test_branch_to_lance_targets_branch(tmp_path):
     assert table.to_lance().count_rows() == 1
 
 
+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, match=r"lancedb\[pylance\]"):
+            table.to_lance()
+
+
 @pytest.mark.asyncio
 async def test_async_to_lance(tmp_path):
     pytest.importorskip("lance")
@@ -1269,6 +1277,16 @@ 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, match=r"lancedb\[pylance\]"):
+            await table.to_lance()
+
+
 @pytest.mark.asyncio
 async def test_async_branch_to_lance_targets_branch(tmp_path):
     pytest.importorskip("lance")