GH-44712: [Python] Convert NumPy integer arrays to decimal types

python/pyarrow/src/arrow/python/numpy_to_arrow.cc

@@ -238,6 +238,8 @@ class NumPyConverter {
 
   Status Visit(const FixedSizeBinaryType& type);
 
+  Status Visit(const DecimalType& type);
+
   // Default case
   Status Visit(const DataType& type) { return TypeNotImplemented(type.ToString()); }
 
@@ -638,6 +640,31 @@ Status NumPyConverter::Visit(const BinaryViewType& type) {
   return PushArray(result->data());
 }
 
+Status NumPyConverter::Visit(const DecimalType& type) {
+  // Decimal types derive from FixedSizeBinaryType, so without this overload
+  // integer arrays would be reinterpreted as raw bytes.
+  if (!PyTypeNum_ISINTEGER(dtype_->type_num)) {
+    return TypeNotImplemented(type.ToString());
+  }
+  ARROW_ASSIGN_OR_RAISE(auto input_type, NumPyDtypeToArrow(dtype_));
+  NumPyConverter converter(pool_, reinterpret_cast<PyObject*>(arr_),
+                           reinterpret_cast<PyObject*>(mask_), input_type, from_pandas_,
+                           cast_options_);
+  RETURN_NOT_OK(converter.Convert());
+  // Go through decimal128(20, 0), which holds any 64-bit integer, so the
+  // final cast checks the values rather than the input type's range.
+  const auto wide_type = decimal128(20, 0);
+  compute::ExecContext context(pool_);
+  for (const auto& arr : converter.result()) {
+    ARROW_ASSIGN_OR_RAISE(auto wide,
+                          compute::Cast(*arr, wide_type, cast_options_, &context));
+    ARROW_ASSIGN_OR_RAISE(auto casted,
+                          compute::Cast(*wide, type_, cast_options_, &context));
+    out_arrays_.push_back(std::move(casted));
+  }
+  return Status::OK();
+}
+
 Status NumPyConverter::Visit(const FixedSizeBinaryType& type) {
   auto byte_width = type.byte_width();
 

python/pyarrow/tests/test_array.py

@@ -1882,6 +1882,22 @@ def test_half_float_array_from_python():
         arr = pa.array(['a', 3, None], type=pa.float16())
 
 
+@pytest.mark.numpy
+@pytest.mark.parametrize('typ', [pa.decimal32(9, 2), pa.decimal64(18, 2),
+                                 pa.decimal128(38, 9), pa.decimal256(40, 2)])
+def test_decimal_from_numpy_integers(typ):
+    # GH-44712
+    arr = np.array([1, -2, 3], dtype=np.int64)
+    expected = pa.array([1, -2, 3], type=typ)
+    assert pa.array(arr, type=typ).equals(expected)
+
+    result = pa.array(arr, type=typ, mask=np.array([False, True, False]))
+    assert result.equals(pa.array([1, None, 3], type=typ))
+
+    with pytest.raises(pa.ArrowInvalid):
+        pa.array(np.array([10**6], dtype=np.int64), type=pa.decimal32(5, 2))
+
+
 def test_decimal_to_int_safe():
     safe_cases = [
         (