Fix performance regression

cpp/src/arrow/python/common.h

@@ -173,7 +173,7 @@ struct ARROW_EXPORT PyBytesView {
   PyBytesView(const char* b, Py_ssize_t s, PyObject* obj = nullptr)
       : bytes(b), size(s), ref(obj) {}
 
-  Status FromBinary(PyObject* obj, const std::string& expected_msg) {
+  Status FromBinary(PyObject* obj, const char* expected_msg) {
     if (PyBytes_Check(obj)) {
       this->bytes = PyBytes_AS_STRING(obj);
       this->size = PyBytes_GET_SIZE(obj);

cpp/src/arrow/python/decimal.cc

@@ -196,15 +196,6 @@ Status DecimalMetadata::Update(PyObject* object) {
   return Update(precision, scale);
 }
 
-bool PyFloat_IsNaN(PyObject* obj) {
-  return PyFloat_Check(obj) && std::isnan(PyFloat_AsDouble(obj));
-}
-
-bool PandasObjectIsNull(PyObject* obj) {
-  return obj == Py_None || obj == numpy_nan || PyFloat_IsNaN(obj) ||
-         (internal::PyDecimal_Check(obj) && internal::PyDecimal_ISNAN(obj));
-}
-
 }  // namespace internal
 }  // namespace py
 }  // namespace arrow

cpp/src/arrow/python/helpers.cc

@@ -21,6 +21,7 @@
 #include <typeinfo>
 
 #include "arrow/python/common.h"
+#include "arrow/python/decimal.h"
 #include "arrow/python/helpers.h"
 #include "arrow/util/logging.h"
 
@@ -323,6 +324,15 @@ template Status CIntFromPython(PyObject*, uint16_t*, const std::string&);
 template Status CIntFromPython(PyObject*, uint32_t*, const std::string&);
 template Status CIntFromPython(PyObject*, uint64_t*, const std::string&);
 
+bool PyFloat_IsNaN(PyObject* obj) {
+  return PyFloat_Check(obj) && std::isnan(PyFloat_AsDouble(obj));
+}
+
+bool PandasObjectIsNull(PyObject* obj) {
+  return obj == Py_None || obj == numpy_nan || PyFloat_IsNaN(obj) ||
+         (internal::PyDecimal_Check(obj) && internal::PyDecimal_ISNAN(obj));
+}
+
 }  // namespace internal
 }  // namespace py
 }  // namespace arrow

cpp/src/arrow/python/helpers.h

@@ -102,7 +102,7 @@ std::string PyObject_StdStringRepr(PyObject* obj);
 
 // \brief Cast the given size to int32_t, with error checking
 inline Status CastSize(Py_ssize_t size, int32_t* out,
-                       const std::string& error_msg = "Maximum size exceeded (2GB)") {
+                       const char* error_msg = "Maximum size exceeded (2GB)") {
   // size is assumed to be positive
   if (size > std::numeric_limits<int32_t>::max()) {
     return Status::Invalid(error_msg);

python/pyarrow/lib.pyx

@@ -33,10 +33,6 @@ from pyarrow.includes.common cimport PyObject_to_object
 cimport pyarrow.includes.libarrow as libarrow
 cimport cpython as cp
 
-cdef _pandas():
-    import pandas as pd
-    return pd
-
 arrow_init_numpy()
 set_numpy_nan(np.nan)