From 731544a04d7d45d23a307e33c60d285292286111 Mon Sep 17 00:00:00 2001
From: Wes McKinney <wesm@apache.org>
Date: Sun, 6 Mar 2016 20:10:44 -0800
Subject: [PATCH] Move PrimitiveType::ToString template back to type.h

---
 cpp/src/arrow/type.cc                      | 9 ---------
 cpp/src/arrow/type.h                       | 9 +++++++++
 python/arrow/__init__.py                   | 3 ++-
 python/arrow/array.pyx                     | 5 +++++
 python/arrow/includes/arrow.pxd            | 2 ++
 python/arrow/schema.pyx                    | 3 +++
 python/arrow/tests/test_convert_builtin.py | 5 +++++
 python/src/pyarrow/adapters/builtin.cc     | 8 ++++++++
 8 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/cpp/src/arrow/type.cc b/cpp/src/arrow/type.cc
index cfed238dc416e..265770822ce90 100644
--- a/cpp/src/arrow/type.cc
+++ b/cpp/src/arrow/type.cc
@@ -30,15 +30,6 @@ std::string Field::ToString() const {
 
 DataType::~DataType() {}
 
-template <typename Derived>
-inline std::string PrimitiveType<Derived>::ToString() const {
-  std::string result(static_cast<const Derived*>(this)->name());
-  if (!nullable) {
-    result.append(" not null");
-  }
-  return result;
-}
-
 StringType::StringType(bool nullable)
     : DataType(LogicalType::STRING, nullable) {}
 
diff --git a/cpp/src/arrow/type.h b/cpp/src/arrow/type.h
index e078e2e656ba3..e78e49491193e 100644
--- a/cpp/src/arrow/type.h
+++ b/cpp/src/arrow/type.h
@@ -221,6 +221,15 @@ struct PrimitiveType : public DataType {
   std::string ToString() const override;
 };
 
+template <typename Derived>
+inline std::string PrimitiveType<Derived>::ToString() const {
+  std::string result(static_cast<const Derived*>(this)->name());
+  if (!nullable) {
+    result.append(" not null");
+  }
+  return result;
+}
+
 #define PRIMITIVE_DECL(TYPENAME, C_TYPE, ENUM, SIZE, NAME)          \
   typedef C_TYPE c_type;                                            \
   static constexpr LogicalType::type type_enum = LogicalType::ENUM; \
diff --git a/python/arrow/__init__.py b/python/arrow/__init__.py
index 41bc8971d39c7..e59c6fda40b44 100644
--- a/python/arrow/__init__.py
+++ b/python/arrow/__init__.py
@@ -18,7 +18,8 @@
 # flake8: noqa
 
 from arrow.array import Array, from_list
-from arrow.schema import (bool_, int8, int16, int32, int64,
+from arrow.schema import (null, bool_,
+                          int8, int16, int32, int64,
                           uint8, uint16, uint32, uint64,
                           float_, double, string,
                           list_, struct, field,
diff --git a/python/arrow/array.pyx b/python/arrow/array.pyx
index cf396da0ef962..2845c9bdec1b2 100644
--- a/python/arrow/array.pyx
+++ b/python/arrow/array.pyx
@@ -39,6 +39,10 @@ cdef class Array:
         return self.array.length()
 
 
+cdef class NullArray(Array):
+    pass
+
+
 cdef class BooleanArray(Array):
     pass
 
@@ -88,6 +92,7 @@ cdef class StringArray(Array):
 
 
 cdef dict _array_classes = {
+    LogicalType_NA: NullArray,
     LogicalType_BOOL: BooleanArray,
     LogicalType_INT64: Int64Array,
     LogicalType_LIST: ListArray,
diff --git a/python/arrow/includes/arrow.pxd b/python/arrow/includes/arrow.pxd
index 666bafc3dad5c..a1a8c25467a24 100644
--- a/python/arrow/includes/arrow.pxd
+++ b/python/arrow/includes/arrow.pxd
@@ -22,6 +22,8 @@ from arrow.includes.common cimport *
 cdef extern from "arrow/api.h" namespace "arrow" nogil:
 
     enum LogicalType" arrow::LogicalType::type":
+        LogicalType_NA" arrow::LogicalType::NA"
+
         LogicalType_BOOL" arrow::LogicalType::BOOL"
 
         LogicalType_UINT8" arrow::LogicalType::UINT8"
diff --git a/python/arrow/schema.pyx b/python/arrow/schema.pyx
index ffb159ab3d4d5..d22c3937efc13 100644
--- a/python/arrow/schema.pyx
+++ b/python/arrow/schema.pyx
@@ -74,6 +74,9 @@ cdef DataType primitive_type(LogicalType type, bint nullable=True):
 def field(name, type):
     return Field(name, type)
 
+def null():
+    return primitive_type(LogicalType_NA)
+
 def bool_(c_bool nullable=True):
     return primitive_type(LogicalType_BOOL, nullable)
 
diff --git a/python/arrow/tests/test_convert_builtin.py b/python/arrow/tests/test_convert_builtin.py
index f88e3cdad5ee3..68875d5b39ddb 100644
--- a/python/arrow/tests/test_convert_builtin.py
+++ b/python/arrow/tests/test_convert_builtin.py
@@ -24,6 +24,11 @@ class TestConvertList(unittest.TestCase):
     def test_boolean(self):
         pass
 
+    def test_empty_list(self):
+        arr = arrow.from_list([])
+        assert len(arr) == 0
+        assert arr.type == arrow.null()
+
     def test_integer(self):
         arr = arrow.from_list([1, 2, 3])
         assert len(arr) == 3
diff --git a/python/src/pyarrow/adapters/builtin.cc b/python/src/pyarrow/adapters/builtin.cc
index fb3b07ccffc23..e8429fd491219 100644
--- a/python/src/pyarrow/adapters/builtin.cc
+++ b/python/src/pyarrow/adapters/builtin.cc
@@ -229,6 +229,12 @@ Status ConvertPySequence(PyObject* obj, std::shared_ptr<arrow::Array>* out) {
   int64_t size;
   RETURN_NOT_OK(InferArrowType(obj, &size, &type));
 
+  // Handle NA / NullType case
+  if (type->type == LogicalType::NA) {
+    out->reset(new arrow::Array(type, size));
+    return Status::OK();
+  }
+
   std::shared_ptr<SeqConverter> converter = GetConverter(type);
   if (converter == nullptr) {
     std::stringstream ss;
@@ -244,6 +250,8 @@ Status ConvertPySequence(PyObject* obj, std::shared_ptr<arrow::Array>* out) {
 
   RETURN_NOT_OK(converter->AppendData(obj));
 
+  *out = builder->Finish();
+
   return Status::OK();
 }