From 0220f3af17325bb64ea2cc5a953159caa7680640 Mon Sep 17 00:00:00 2001
From: Wyatt Alt <wyatt.alt@gmail.com>
Date: Sun, 18 Oct 2026 11:13:18 -0700
Subject: [PATCH] feat(python): accept large_binary in Function signatures
 (#4577)

udf() rejected a large_binary input or output, and large_binary nested in a list or struct, outside a Blob v2 payload. It is now a grammar primitive like large_utf8, and the shared type golden lists it.
---
 python/python/lancedb/functions.py            |  7 ++----
 .../tests/test_first_class_function_slice2.py | 23 ++++++++++++++++++-
 .../first_class_functions/v1/arrow_types.json | 21 +++++++++++++++++
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/python/python/lancedb/functions.py b/python/python/lancedb/functions.py
index 445d31027..7f5776b32 100644
--- a/python/python/lancedb/functions.py
+++ b/python/python/lancedb/functions.py
@@ -697,6 +697,7 @@ _GRAMMAR_PRIMITIVES = (
     (pa.string(), "utf8"),
     (pa.large_string(), "large_utf8"),
     (pa.binary(), "binary"),
+    (pa.large_binary(), "large_binary"),
     (pa.date32(), "date32"),
     (pa.date64(), "date64"),
 )
@@ -846,11 +847,7 @@ def _exact_blob_storage_type(field: pa.Field) -> dict[str, Any]:
             {
                 "name": child.name,
                 "nullable": child.nullable,
-                "type": (
-                    {"type": "large_binary"}
-                    if pa.types.is_large_binary(child.type)
-                    else _exact_arrow_type(child.type)
-                ),
+                "type": _exact_arrow_type(child.type),
             }
             for child in storage
         ],
diff --git a/python/python/tests/test_first_class_function_slice2.py b/python/python/tests/test_first_class_function_slice2.py
index 975310ed4..9ee3e388a 100644
--- a/python/python/tests/test_first_class_function_slice2.py
+++ b/python/python/tests/test_first_class_function_slice2.py
@@ -622,7 +622,6 @@ def test_canonical_arrow_type_prefers_the_compact_grammar():
     for outside in [
         pa.timestamp("us"),
         pa.decimal128(10, 2),
-        pa.large_binary(),
         pa.binary(4),
         pa.duration("s"),
         pa.list_(pa.float32(), 0),
@@ -1280,6 +1279,28 @@ def test_explicit_large_utf8_schemas_use_the_canonical_function_name():
     }
 
 
+def test_large_binary_schemas_use_the_canonical_function_name():
+    payload = pa.field("data", pa.large_binary(), nullable=True)
+
+    @udf(
+        input_schema=pa.schema([payload]),
+        output_schema=pa.field("result", pa.large_binary(), nullable=False),
+    )
+    def preserve(data):
+        return data
+
+    signature = preserve.registration_request.signature
+    assert signature.inputs[0].arrow_type == "large_binary"
+    assert signature.output.arrow_type == "large_binary"
+    cells = pa.large_list(pa.field("item", pa.struct([payload]), nullable=True))
+    assert json.loads(_canonical_arrow_type(cells))["fields"][0]["type"] == {
+        "type": "struct",
+        "fields": [
+            {"name": "data", "nullable": True, "type": {"type": "large_binary"}}
+        ],
+    }
+
+
 def test_nested_struct_output_uses_canonical_exact_json():
     token = pa.struct(
         [
diff --git a/rust/lancedb/tests/fixtures/first_class_functions/v1/arrow_types.json b/rust/lancedb/tests/fixtures/first_class_functions/v1/arrow_types.json
index 38d17821b..26e8db430 100644
--- a/rust/lancedb/tests/fixtures/first_class_functions/v1/arrow_types.json
+++ b/rust/lancedb/tests/fixtures/first_class_functions/v1/arrow_types.json
@@ -90,6 +90,12 @@
         "type": "binary"
       }
     },
+    {
+      "arrow_type": "large_binary",
+      "json": {
+        "type": "large_binary"
+      }
+    },
     {
       "arrow_type": "date32",
       "json": {
@@ -192,6 +198,21 @@
         ]
       }
     },
+    {
+      "arrow_type": "large_list<large_binary>",
+      "json": {
+        "type": "large_list",
+        "fields": [
+          {
+            "name": "item",
+            "nullable": false,
+            "type": {
+              "type": "large_binary"
+            }
+          }
+        ]
+      }
+    },
     {
       "arrow_type": "large_list<utf8>",
       "json": {