From 1e909303b8646e9081dd40902337f4710072d32b Mon Sep 17 00:00:00 2001
From: anjakefala <anja.kefala@gmail.com>
Date: Thu, 14 Mar 2024 16:51:11 -0400
Subject: [PATCH] GH-40316: [Python] only allocate the ScalarMemoTable when
 used

---
 .../src/arrow/python/arrow_to_pandas.cc       | 61 ++++++++++---------
 1 file changed, 33 insertions(+), 28 deletions(-)

diff --git a/python/pyarrow/src/arrow/python/arrow_to_pandas.cc b/python/pyarrow/src/arrow/python/arrow_to_pandas.cc
index cb9cbe5b930e7..876ec50a179df 100644
--- a/python/pyarrow/src/arrow/python/arrow_to_pandas.cc
+++ b/python/pyarrow/src/arrow/python/arrow_to_pandas.cc
@@ -620,37 +620,42 @@ inline Status ConvertAsPyObjects(const PandasOptions& options, const ChunkedArra
   using ArrayType = typename TypeTraits<Type>::ArrayType;
   using Scalar = typename MemoizationTraits<Type>::Scalar;
 
-  ::arrow::internal::ScalarMemoTable<Scalar> memo_table(options.pool);
-  std::vector<PyObject*> unique_values;
-  int32_t memo_size = 0;
-
-  auto WrapMemoized = [&](const Scalar& value, PyObject** out_values) {
-    int32_t memo_index;
-    RETURN_NOT_OK(memo_table.GetOrInsert(value, &memo_index));
-    if (memo_index == memo_size) {
-      // New entry
-      RETURN_NOT_OK(wrap_func(value, out_values));
-      unique_values.push_back(*out_values);
-      ++memo_size;
-    } else {
-      // Duplicate entry
-      Py_INCREF(unique_values[memo_index]);
-      *out_values = unique_values[memo_index];
-    }
-    return Status::OK();
-  };
-
-  auto WrapUnmemoized = [&](const Scalar& value, PyObject** out_values) {
-    return wrap_func(value, out_values);
-  };
+  std::shared_ptr<::arrow::internal::ScalarMemoTable<Scalar>> memo_table = nullptr;
+  std::shared_ptr<std::vector<PyObject*>> unique_values = nullptr;
+  std::shared_ptr<int32_t> memo_size = std::make_shared<int32_t>(0);
+
+  std::function<Status(const typename MemoizationTraits<Type>::Scalar&, PyObject**)>
+    WrapFunc;
+
+  if (options.deduplicate_objects) {
+    memo_table =
+      std::make_shared<::arrow::internal::ScalarMemoTable<Scalar>>(options.pool);
+    unique_values = std::make_shared<std::vector<PyObject*>>();
+
+    WrapFunc = [&](const Scalar& value, PyObject** out_values) {
+      int32_t memo_index;
+      RETURN_NOT_OK(memo_table->GetOrInsert(value, &memo_index));
+      if (memo_index == *memo_size) {
+        // New entry
+        RETURN_NOT_OK(wrap_func(value, out_values));
+        unique_values->push_back(*out_values);
+        ++(*memo_size);
+      } else {
+        // Duplicate entry
+        Py_INCREF((*unique_values)[memo_index]);
+        *out_values = (*unique_values)[memo_index];
+      }
+      return Status::OK();
+    };
+  } else {
+    WrapFunc = [&](const Scalar& value, PyObject** out_values) {
+      return wrap_func(value, out_values);
+    };
+  }
 
   for (int c = 0; c < data.num_chunks(); c++) {
     const auto& arr = arrow::internal::checked_cast<const ArrayType&>(*data.chunk(c));
-    if (options.deduplicate_objects) {
-      RETURN_NOT_OK(internal::WriteArrayObjects(arr, WrapMemoized, out_values));
-    } else {
-      RETURN_NOT_OK(internal::WriteArrayObjects(arr, WrapUnmemoized, out_values));
-    }
+    RETURN_NOT_OK(internal::WriteArrayObjects(arr, WrapFunc, out_values));
     out_values += arr.length();
   }
   return Status::OK();