fix(python): invalid namespace mode/behavior was silently ignored, now raises ValueError (#3388)

Follow-up to #3371 , which added runtime validation for namespace `mode`
and `behavior` parameters in the NodeJS SDK. Bringing the same fix to
Python for cross-SDK consistency.

**Before:** unrecognized values were silently dropped to `None`, so
`db.create_namespace(["x"], mode="foobar")` would quietly fall through
to the server's default mode and hide caller typos.

**After:** raises `ValueError` listing the valid values.

python/python/lancedb/namespace_utils.py

@@ -6,22 +6,44 @@
 from typing import Optional
 
 
+_CREATE_NAMESPACE_MODES = frozenset({"create", "exist_ok", "overwrite"})
+_DROP_NAMESPACE_MODES = frozenset({"SKIP", "FAIL"})
+_DROP_NAMESPACE_BEHAVIORS = frozenset({"RESTRICT", "CASCADE"})
+
+
 def _normalize_create_namespace_mode(mode: Optional[str]) -> Optional[str]:
     """Normalize create namespace mode to lowercase (API expects lowercase)."""
     if mode is None:
         return None
-    return mode.lower()
+    normalized = mode.lower()
+    if normalized not in _CREATE_NAMESPACE_MODES:
+        raise ValueError(
+            f"Invalid create namespace mode {mode!r}: "
+            f"expected one of 'create', 'exist_ok', 'overwrite'"
+        )
+    return normalized
 
 
 def _normalize_drop_namespace_mode(mode: Optional[str]) -> Optional[str]:
     """Normalize drop namespace mode to uppercase (API expects uppercase)."""
     if mode is None:
         return None
-    return mode.upper()
+    normalized = mode.upper()
+    if normalized not in _DROP_NAMESPACE_MODES:
+        raise ValueError(
+            f"Invalid drop namespace mode {mode!r}: expected one of 'skip', 'fail'"
+        )
+    return normalized
 
 
 def _normalize_drop_namespace_behavior(behavior: Optional[str]) -> Optional[str]:
     """Normalize drop namespace behavior to uppercase (API expects uppercase)."""
     if behavior is None:
         return None
-    return behavior.upper()
+    normalized = behavior.upper()
+    if normalized not in _DROP_NAMESPACE_BEHAVIORS:
+        raise ValueError(
+            f"Invalid drop namespace behavior {behavior!r}: "
+            f"expected one of 'restrict', 'cascade'"
+        )
+    return normalized

python/python/tests/test_db.py

@@ -914,6 +914,29 @@ def test_local_namespace_operations(tmp_path):
     assert db.list_namespaces().namespaces == []
 
 
+def test_create_namespace_invalid_mode_raises(tmp_path):
+    """Unrecognized create namespace modes raise a clear error."""
+    db = lancedb.connect(tmp_path)
+    with pytest.raises(ValueError, match="Invalid create namespace mode"):
+        db.create_namespace(["child"], mode="frobnicate")
+
+
+def test_drop_namespace_invalid_mode_raises(tmp_path):
+    """Unrecognized drop namespace modes raise a clear error."""
+    db = lancedb.connect(tmp_path)
+    db.create_namespace(["child"])
+    with pytest.raises(ValueError, match="Invalid drop namespace mode"):
+        db.drop_namespace(["child"], mode="frobnicate")
+
+
+def test_drop_namespace_invalid_behavior_raises(tmp_path):
+    """Unrecognized drop namespace behaviors raise a clear error."""
+    db = lancedb.connect(tmp_path)
+    db.create_namespace(["child"])
+    with pytest.raises(ValueError, match="Invalid drop namespace behavior"):
+        db.drop_namespace(["child"], behavior="frobnicate")
+
+
 def test_clone_table_latest_version(tmp_path):
     """Test cloning a table with the latest version (default behavior)"""
     import os