Integrated internal changes from Google

8 files changed, 577 insertions, 244 deletions

diff --git a/python/google/protobuf/pyext/descriptor_pool.cc b/python/google/protobuf/pyext/descriptor_pool.cc
index a42e5431..fa66bf9a 100644
--- a/python/google/protobuf/pyext/descriptor_pool.cc
+++ b/python/google/protobuf/pyext/descriptor_pool.cc
@@ -319,6 +319,51 @@ PyObject* FindFileContainingSymbol(PyDescriptorPool* self, PyObject* arg) {
   return PyFileDescriptor_FromDescriptor(file_descriptor);
 }
 
+PyObject* FindExtensionByNumber(PyDescriptorPool* self, PyObject* args) {
+  PyObject* message_descriptor;
+  int number;
+  if (!PyArg_ParseTuple(args, "Oi", &message_descriptor, &number)) {
+    return NULL;
+  }
+  const Descriptor* descriptor = PyMessageDescriptor_AsDescriptor(
+      message_descriptor);
+  if (descriptor == NULL) {
+    return NULL;
+  }
+
+  const FieldDescriptor* extension_descriptor =
+      self->pool->FindExtensionByNumber(descriptor, number);
+  if (extension_descriptor == NULL) {
+    PyErr_Format(PyExc_KeyError, "Couldn't find extension %d", number);
+    return NULL;
+  }
+
+  return PyFieldDescriptor_FromDescriptor(extension_descriptor);
+}
+
+PyObject* FindAllExtensions(PyDescriptorPool* self, PyObject* arg) {
+  const Descriptor* descriptor = PyMessageDescriptor_AsDescriptor(arg);
+  if (descriptor == NULL) {
+    return NULL;
+  }
+
+  std::vector<const FieldDescriptor*> extensions;
+  self->pool->FindAllExtensions(descriptor, &extensions);
+
+  ScopedPyObjectPtr result(PyList_New(extensions.size()));
+  if (result == NULL) {
+    return NULL;
+  }
+  for (int i = 0; i < extensions.size(); i++) {
+    PyObject* extension = PyFieldDescriptor_FromDescriptor(extensions[i]);
+    if (extension == NULL) {
+      return NULL;
+    }
+    PyList_SET_ITEM(result.get(), i, extension);  // Steals the reference.
+  }
+  return result.release();
+}
+
 // These functions should not exist -- the only valid way to create
 // descriptors is to call Add() or AddSerializedFile().
 // But these AddDescriptor() functions were created in Python and some people
@@ -376,6 +421,22 @@ PyObject* AddEnumDescriptor(PyDescriptorPool* self, PyObject* descriptor) {
   Py_RETURN_NONE;
 }
 
+PyObject* AddExtensionDescriptor(PyDescriptorPool* self, PyObject* descriptor) {
+  const FieldDescriptor* extension_descriptor =
+      PyFieldDescriptor_AsDescriptor(descriptor);
+  if (!extension_descriptor) {
+    return NULL;
+  }
+  if (extension_descriptor !=
+      self->pool->FindExtensionByName(extension_descriptor->full_name())) {
+    PyErr_Format(PyExc_ValueError,
+                 "The extension descriptor %s does not belong to this pool",
+                 extension_descriptor->full_name().c_str());
+    return NULL;
+  }
+  Py_RETURN_NONE;
+}
+
 // The code below loads new Descriptors from a serialized FileDescriptorProto.
 
 
@@ -475,6 +536,8 @@ static PyMethodDef Methods[] = {
     "No-op. Add() must have been called before." },
   { "AddEnumDescriptor", (PyCFunction)AddEnumDescriptor, METH_O,
     "No-op. Add() must have been called before." },
+  { "AddExtensionDescriptor", (PyCFunction)AddExtensionDescriptor, METH_O,
+    "No-op. Add() must have been called before." },
 
   { "FindFileByName", (PyCFunction)FindFileByName, METH_O,
     "Searches for a file descriptor by its .proto name." },
@@ -495,6 +558,10 @@ static PyMethodDef Methods[] = {
 
   { "FindFileContainingSymbol", (PyCFunction)FindFileContainingSymbol, METH_O,
     "Gets the FileDescriptor containing the specified symbol." },
+  { "FindExtensionByNumber", (PyCFunction)FindExtensionByNumber, METH_VARARGS,
+    "Gets the extension descriptor for the given number." },
+  { "FindAllExtensions", (PyCFunction)FindAllExtensions, METH_O,
+    "Gets all known extensions of the given message descriptor." },
   {NULL}
 };
 
diff --git a/python/google/protobuf/pyext/extension_dict.cc b/python/google/protobuf/pyext/extension_dict.cc
index dbb7bca0..9423c1d8 100644
--- a/python/google/protobuf/pyext/extension_dict.cc
+++ b/python/google/protobuf/pyext/extension_dict.cc
@@ -38,6 +38,7 @@
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/dynamic_message.h>
 #include <google/protobuf/message.h>
+#include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/pyext/descriptor.h>
 #include <google/protobuf/pyext/message.h>
 #include <google/protobuf/pyext/message_factory.h>
@@ -46,6 +47,16 @@
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 #include <google/protobuf/stubs/shared_ptr.h>
 
+#if PY_MAJOR_VERSION >= 3
+  #if PY_VERSION_HEX < 0x03030000
+    #error "Python 3.0 - 3.2 are not supported."
+  #endif
+  #define PyString_AsStringAndSize(ob, charpp, sizep) \
+    (PyUnicode_Check(ob)? \
+       ((*(charpp) = PyUnicode_AsUTF8AndSize(ob, (sizep))) == NULL? -1: 0): \
+       PyBytes_AsStringAndSize(ob, (charpp), (sizep)))
+#endif
+
 namespace google {
 namespace protobuf {
 namespace python {
@@ -90,6 +101,7 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
 
   if (descriptor->label() != FieldDescriptor::LABEL_REPEATED &&
       descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
+    // TODO(plabatut): consider building the class on the fly!
     PyObject* sub_message = cmessage::InternalGetSubMessage(
         self->parent, descriptor);
     if (sub_message == NULL) {
@@ -101,7 +113,17 @@ PyObject* subscript(ExtensionDict* self, PyObject* key) {
 
   if (descriptor->label() == FieldDescriptor::LABEL_REPEATED) {
     if (descriptor->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      CMessageClass* message_class = message_factory::GetMessageClass(
+      // On the fly message class creation is needed to support the following
+      // situation:
+      // 1- add FileDescriptor to the pool that contains extensions of a message
+      //    defined by another proto file. Do not create any message classes.
+      // 2- instantiate an extended message, and access the extension using
+      //    the field descriptor.
+      // 3- the extension submessage fails to be returned, because no class has
+      //    been created.
+      // It happens when deserializing text proto format, or when enumerating
+      // fields of a deserialized message.
+      CMessageClass* message_class = message_factory::GetOrCreateMessageClass(
           cmessage::GetFactoryForMessage(self->parent),
           descriptor->message_type());
       if (message_class == NULL) {
@@ -154,34 +176,51 @@ int ass_subscript(ExtensionDict* self, PyObject* key, PyObject* value) {
   return 0;
 }
 
-PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* name) {
-  ScopedPyObjectPtr extensions_by_name(PyObject_GetAttrString(
-      reinterpret_cast<PyObject*>(self->parent), "_extensions_by_name"));
-  if (extensions_by_name == NULL) {
+PyObject* _FindExtensionByName(ExtensionDict* self, PyObject* arg) {
+  char* name;
+  Py_ssize_t name_size;
+  if (PyString_AsStringAndSize(arg, &name, &name_size) < 0) {
     return NULL;
   }
-  PyObject* result = PyDict_GetItem(extensions_by_name.get(), name);
-  if (result == NULL) {
+
+  PyDescriptorPool* pool = cmessage::GetFactoryForMessage(self->parent)->pool;
+  const FieldDescriptor* message_extension =
+      pool->pool->FindExtensionByName(string(name, name_size));
+  if (message_extension == NULL) {
+    // Is is the name of a message set extension?
+    const Descriptor* message_descriptor = pool->pool->FindMessageTypeByName(
+        string(name, name_size));
+    if (message_descriptor && message_descriptor->extension_count() > 0) {
+      const FieldDescriptor* extension = message_descriptor->extension(0);
+      if (extension->is_extension() &&
+          extension->containing_type()->options().message_set_wire_format() &&
+          extension->type() == FieldDescriptor::TYPE_MESSAGE &&
+          extension->label() == FieldDescriptor::LABEL_OPTIONAL) {
+        message_extension = extension;
+      }
+    }
+  }
+  if (message_extension == NULL) {
     Py_RETURN_NONE;
-  } else {
-    Py_INCREF(result);
-    return result;
   }
+
+  return PyFieldDescriptor_FromDescriptor(message_extension);
 }
 
-PyObject* _FindExtensionByNumber(ExtensionDict* self, PyObject* number) {
-  ScopedPyObjectPtr extensions_by_number(PyObject_GetAttrString(
-      reinterpret_cast<PyObject*>(self->parent), "_extensions_by_number"));
-  if (extensions_by_number == NULL) {
+PyObject* _FindExtensionByNumber(ExtensionDict* self, PyObject* arg) {
+  int64 number = PyLong_AsLong(arg);
+  if (number == -1 && PyErr_Occurred()) {
     return NULL;
   }
-  PyObject* result = PyDict_GetItem(extensions_by_number.get(), number);
-  if (result == NULL) {
+
+  PyDescriptorPool* pool = cmessage::GetFactoryForMessage(self->parent)->pool;
+  const FieldDescriptor* message_extension = pool->pool->FindExtensionByNumber(
+      self->parent->message->GetDescriptor(), number);
+  if (message_extension == NULL) {
     Py_RETURN_NONE;
-  } else {
-    Py_INCREF(result);
-    return result;
   }
+
+  return PyFieldDescriptor_FromDescriptor(message_extension);
 }
 
 ExtensionDict* NewExtensionDict(CMessage *parent) {
diff --git a/python/google/protobuf/pyext/map_container.cc b/python/google/protobuf/pyext/map_container.cc
index 318c2e7c..088ddf93 100644
--- a/python/google/protobuf/pyext/map_container.cc
+++ b/python/google/protobuf/pyext/map_container.cc
@@ -374,7 +374,7 @@ static int InitializeAndCopyToParentContainer(MapContainer* from,
     // A somewhat roundabout way of copying just one field from old_message to
     // new_message.  This is the best we can do with what Reflection gives us.
     Message* mutable_old = from->GetMutableMessage();
-    vector<const FieldDescriptor*> fields;
+    std::vector<const FieldDescriptor*> fields;
     fields.push_back(from->parent_field_descriptor);
 
     // Move the map field into the new message.
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index 7ff99aea..5967a587 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -64,11 +64,11 @@
 #include <google/protobuf/pyext/repeated_scalar_container.h>
 #include <google/protobuf/pyext/map_container.h>
 #include <google/protobuf/pyext/message_factory.h>
+#include <google/protobuf/pyext/safe_numerics.h>
 #include <google/protobuf/pyext/scoped_pyobject_ptr.h>
 #include <google/protobuf/stubs/strutil.h>
 
 #if PY_MAJOR_VERSION >= 3
-  #define PyInt_Check PyLong_Check
   #define PyInt_AsLong PyLong_AsLong
   #define PyInt_FromLong PyLong_FromLong
   #define PyInt_FromSize_t PyLong_FromSize_t
@@ -92,8 +92,6 @@ namespace protobuf {
 namespace python {
 
 static PyObject* kDESCRIPTOR;
-static PyObject* k_extensions_by_name;
-static PyObject* k_extensions_by_number;
 PyObject* EnumTypeWrapper_class;
 static PyObject* PythonMessage_class;
 static PyObject* kEmptyWeakref;
@@ -128,19 +126,6 @@ static bool AddFieldNumberToClass(
 
 // Finalize the creation of the Message class.
 static int AddDescriptors(PyObject* cls, const Descriptor* descriptor) {
-  // If there are extension_ranges, the message is "extendable", and extension
-  // classes will register themselves in this class.
-  if (descriptor->extension_range_count() > 0) {
-    ScopedPyObjectPtr by_name(PyDict_New());
-    if (PyObject_SetAttr(cls, k_extensions_by_name, by_name.get()) < 0) {
-      return -1;
-    }
-    ScopedPyObjectPtr by_number(PyDict_New());
-    if (PyObject_SetAttr(cls, k_extensions_by_number, by_number.get()) < 0) {
-      return -1;
-    }
-  }
-
   // For each field set: cls.<field>_FIELD_NUMBER = <number>
   for (int i = 0; i < descriptor->field_count(); ++i) {
     if (!AddFieldNumberToClass(cls, descriptor->field(i))) {
@@ -357,6 +342,61 @@ static int InsertEmptyWeakref(PyTypeObject *base_type) {
 #endif  // PY_MAJOR_VERSION >= 3
 }
 
+// The _extensions_by_name dictionary is built on every access.
+// TODO(amauryfa): Migrate all users to pool.FindAllExtensions()
+static PyObject* GetExtensionsByName(CMessageClass *self, void *closure) {
+  const PyDescriptorPool* pool = self->py_message_factory->pool;
+
+  std::vector<const FieldDescriptor*> extensions;
+  pool->pool->FindAllExtensions(self->message_descriptor, &extensions);
+
+  ScopedPyObjectPtr result(PyDict_New());
+  for (int i = 0; i < extensions.size(); i++) {
+    ScopedPyObjectPtr extension(
+        PyFieldDescriptor_FromDescriptor(extensions[i]));
+    if (extension == NULL) {
+      return NULL;
+    }
+    if (PyDict_SetItemString(result.get(), extensions[i]->full_name().c_str(),
+                             extension.get()) < 0) {
+      return NULL;
+    }
+  }
+  return result.release();
+}
+
+// The _extensions_by_number dictionary is built on every access.
+// TODO(amauryfa): Migrate all users to pool.FindExtensionByNumber()
+static PyObject* GetExtensionsByNumber(CMessageClass *self, void *closure) {
+  const PyDescriptorPool* pool = self->py_message_factory->pool;
+
+  std::vector<const FieldDescriptor*> extensions;
+  pool->pool->FindAllExtensions(self->message_descriptor, &extensions);
+
+  ScopedPyObjectPtr result(PyDict_New());
+  for (int i = 0; i < extensions.size(); i++) {
+    ScopedPyObjectPtr extension(
+        PyFieldDescriptor_FromDescriptor(extensions[i]));
+    if (extension == NULL) {
+      return NULL;
+    }
+    ScopedPyObjectPtr number(PyInt_FromLong(extensions[i]->number()));
+    if (number == NULL) {
+      return NULL;
+    }
+    if (PyDict_SetItem(result.get(), number.get(), extension.get()) < 0) {
+      return NULL;
+    }
+  }
+  return result.release();
+}
+
+static PyGetSetDef Getters[] = {
+  {"_extensions_by_name", (getter)GetExtensionsByName, NULL},
+  {"_extensions_by_number", (getter)GetExtensionsByNumber, NULL},
+  {NULL}
+};
+
 }  // namespace message_meta
 
 PyTypeObject CMessageClass_Type = {
@@ -389,7 +429,7 @@ PyTypeObject CMessageClass_Type = {
   0,                                   // tp_iternext
   0,                                   // tp_methods
   0,                                   // tp_members
-  0,                                   // tp_getset
+  message_meta::Getters,               // tp_getset
   0,                                   // tp_base
   0,                                   // tp_dict
   0,                                   // tp_descr_get
@@ -525,23 +565,10 @@ int ForEachCompositeField(CMessage* self, Visitor visitor) {
 
 // ---------------------------------------------------------------------
 
-// Constants used for integer type range checking.
-PyObject* kPythonZero;
-PyObject* kint32min_py;
-PyObject* kint32max_py;
-PyObject* kuint32max_py;
-PyObject* kint64min_py;
-PyObject* kint64max_py;
-PyObject* kuint64max_py;
-
 PyObject* EncodeError_class;
 PyObject* DecodeError_class;
 PyObject* PickleError_class;
 
-// Constant PyString values used for GetAttr/GetItem.
-static PyObject* k_cdescriptor;
-static PyObject* kfull_name;
-
 /* Is 64bit */
 void FormatTypeError(PyObject* arg, char* expected_types) {
   PyObject* repr = PyObject_Repr(arg);
@@ -555,68 +582,126 @@ void FormatTypeError(PyObject* arg, char* expected_types) {
   }
 }
 
-template<class T>
-bool CheckAndGetInteger(
-    PyObject* arg, T* value, PyObject* min, PyObject* max) {
-  bool is_long = PyLong_Check(arg);
-#if PY_MAJOR_VERSION < 3
-  if (!PyInt_Check(arg) && !is_long) {
-    FormatTypeError(arg, "int, long");
-    return false;
+void OutOfRangeError(PyObject* arg) {
+  PyObject *s = PyObject_Str(arg);
+  if (s) {
+    PyErr_Format(PyExc_ValueError,
+                 "Value out of range: %s",
+                 PyString_AsString(s));
+    Py_DECREF(s);
   }
-  if (PyObject_Compare(min, arg) > 0 || PyObject_Compare(max, arg) < 0) {
-#else
-  if (!is_long) {
-    FormatTypeError(arg, "int");
+}
+
+template<class RangeType, class ValueType>
+bool VerifyIntegerCastAndRange(PyObject* arg, ValueType value) {
+  if GOOGLE_PREDICT_FALSE(value == -1 && PyErr_Occurred()) {
+    if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
+      // Replace it with the same ValueError as pure python protos instead of
+      // the default one.
+      PyErr_Clear();
+      OutOfRangeError(arg);
+    }  // Otherwise propagate existing error.
     return false;
   }
-  if (PyObject_RichCompareBool(min, arg, Py_LE) != 1 ||
-      PyObject_RichCompareBool(max, arg, Py_GE) != 1) {
-#endif
-    if (!PyErr_Occurred()) {
-      PyObject *s = PyObject_Str(arg);
-      if (s) {
-        PyErr_Format(PyExc_ValueError,
-                     "Value out of range: %s",
-                     PyString_AsString(s));
-        Py_DECREF(s);
-      }
-    }
+  if GOOGLE_PREDICT_FALSE(!IsValidNumericCast<RangeType>(value)) {
+    OutOfRangeError(arg);
     return false;
   }
+  return true;
+}
+
+template<class T>
+bool CheckAndGetInteger(PyObject* arg, T* value) {
+  // The fast path.
 #if PY_MAJOR_VERSION < 3
-  if (!is_long) {
-    *value = static_cast<T>(PyInt_AsLong(arg));
-  } else  // NOLINT
+  // For the typical case, offer a fast path.
+  if GOOGLE_PREDICT_TRUE(PyInt_Check(arg)) {
+    long int_result =  PyInt_AsLong(arg);
+    if GOOGLE_PREDICT_TRUE(IsValidNumericCast<T>(int_result)) {
+      *value = static_cast<T>(int_result);
+      return true;
+    } else {
+      OutOfRangeError(arg);
+      return false;
+    }
+  }
 #endif
-  {
-    if (min == kPythonZero) {
-      *value = static_cast<T>(PyLong_AsUnsignedLongLong(arg));
+  // This effectively defines an integer as "an object that can be cast as
+  // an integer and can be used as an ordinal number".
+  // This definition includes everything that implements numbers.Integral
+  // and shouldn't cast the net too wide.
+  if GOOGLE_PREDICT_FALSE(!PyIndex_Check(arg)) {
+    FormatTypeError(arg, "int, long");
+    return false;
+  }
+
+  // Now we have an integral number so we can safely use PyLong_ functions.
+  // We need to treat the signed and unsigned cases differently in case arg is
+  // holding a value above the maximum for signed longs.
+  if (std::numeric_limits<T>::min() == 0) {
+    // Unsigned case.
+    unsigned PY_LONG_LONG ulong_result;
+    if (PyLong_Check(arg)) {
+      ulong_result = PyLong_AsUnsignedLongLong(arg);
+    } else {
+      // Unlike PyLong_AsLongLong, PyLong_AsUnsignedLongLong is very
+      // picky about the exact type.
+      PyObject* casted = PyNumber_Long(arg);
+      if GOOGLE_PREDICT_FALSE(casted == NULL) {
+        // Propagate existing error.
+        return false;
+      }
+      ulong_result = PyLong_AsUnsignedLongLong(casted);
+      Py_DECREF(casted);
+    }
+    if (VerifyIntegerCastAndRange<T, unsigned PY_LONG_LONG>(arg,
+                                                            ulong_result)) {
+      *value = static_cast<T>(ulong_result);
+    } else {
+      return false;
+    }
+  } else {
+    // Signed case.
+    PY_LONG_LONG long_result;
+    PyNumberMethods *nb;
+    if ((nb = arg->ob_type->tp_as_number) != NULL && nb->nb_int != NULL) {
+      // PyLong_AsLongLong requires it to be a long or to have an __int__()
+      // method.
+      long_result = PyLong_AsLongLong(arg);
     } else {
-      *value = static_cast<T>(PyLong_AsLongLong(arg));
+      // Valid subclasses of numbers.Integral should have a __long__() method
+      // so fall back to that.
+      PyObject* casted = PyNumber_Long(arg);
+      if GOOGLE_PREDICT_FALSE(casted == NULL) {
+        // Propagate existing error.
+        return false;
+      }
+      long_result = PyLong_AsLongLong(casted);
+      Py_DECREF(casted);
+    }
+    if (VerifyIntegerCastAndRange<T, PY_LONG_LONG>(arg, long_result)) {
+      *value = static_cast<T>(long_result);
+    } else {
+      return false;
     }
   }
+
   return true;
 }
 
 // These are referenced by repeated_scalar_container, and must
 // be explicitly instantiated.
-template bool CheckAndGetInteger<int32>(
-    PyObject*, int32*, PyObject*, PyObject*);
-template bool CheckAndGetInteger<int64>(
-    PyObject*, int64*, PyObject*, PyObject*);
-template bool CheckAndGetInteger<uint32>(
-    PyObject*, uint32*, PyObject*, PyObject*);
-template bool CheckAndGetInteger<uint64>(
-    PyObject*, uint64*, PyObject*, PyObject*);
+template bool CheckAndGetInteger<int32>(PyObject*, int32*);
+template bool CheckAndGetInteger<int64>(PyObject*, int64*);
+template bool CheckAndGetInteger<uint32>(PyObject*, uint32*);
+template bool CheckAndGetInteger<uint64>(PyObject*, uint64*);
 
 bool CheckAndGetDouble(PyObject* arg, double* value) {
-  if (!PyInt_Check(arg) && !PyLong_Check(arg) &&
-      !PyFloat_Check(arg)) {
+  *value = PyFloat_AsDouble(arg);
+  if GOOGLE_PREDICT_FALSE(*value == -1 && PyErr_Occurred()) {
     FormatTypeError(arg, "int, long, float");
     return false;
   }
-  *value = PyFloat_AsDouble(arg);
   return true;
 }
 
@@ -630,11 +715,13 @@ bool CheckAndGetFloat(PyObject* arg, float* value) {
 }
 
 bool CheckAndGetBool(PyObject* arg, bool* value) {
-  if (!PyInt_Check(arg) && !PyBool_Check(arg) && !PyLong_Check(arg)) {
+  long long_value = PyInt_AsLong(arg);
+  if (long_value == -1 && PyErr_Occurred()) {
     FormatTypeError(arg, "int, long, bool");
     return false;
   }
-  *value = static_cast<bool>(PyInt_AsLong(arg));
+  *value = static_cast<bool>(long_value);
+
   return true;
 }
 
@@ -966,20 +1053,7 @@ int InternalDeleteRepeatedField(
   int min, max;
   length = reflection->FieldSize(*message, field_descriptor);
 
-  if (PyInt_Check(slice) || PyLong_Check(slice)) {
-    from = to = PyLong_AsLong(slice);
-    if (from < 0) {
-      from = to = length + from;
-    }
-    step = 1;
-    min = max = from;
-
-    // Range check.
-    if (from < 0 || from >= length) {
-      PyErr_Format(PyExc_IndexError, "list assignment index out of range");
-      return -1;
-    }
-  } else if (PySlice_Check(slice)) {
+  if (PySlice_Check(slice)) {
     from = to = step = slice_length = 0;
     PySlice_GetIndicesEx(
 #if PY_MAJOR_VERSION < 3
@@ -996,8 +1070,23 @@ int InternalDeleteRepeatedField(
       max = from;
     }
   } else {
-    PyErr_SetString(PyExc_TypeError, "list indices must be integers");
-    return -1;
+    from = to = PyLong_AsLong(slice);
+    if (from == -1 && PyErr_Occurred()) {
+      PyErr_SetString(PyExc_TypeError, "list indices must be integers");
+      return -1;
+    }
+
+    if (from < 0) {
+      from = to = length + from;
+    }
+    step = 1;
+    min = max = from;
+
+    // Range check.
+    if (from < 0 || from >= length) {
+      PyErr_Format(PyExc_IndexError, "list assignment index out of range");
+      return -1;
+    }
   }
 
   Py_ssize_t i = from;
@@ -1958,99 +2047,29 @@ static PyObject* ByteSize(CMessage* self, PyObject* args) {
   return PyLong_FromLong(self->message->ByteSize());
 }
 
-static PyObject* RegisterExtension(PyObject* cls,
-                                   PyObject* extension_handle) {
+PyObject* RegisterExtension(PyObject* cls, PyObject* extension_handle) {
   const FieldDescriptor* descriptor =
       GetExtensionDescriptor(extension_handle);
   if (descriptor == NULL) {
     return NULL;
   }
-
-  ScopedPyObjectPtr extensions_by_name(
-      PyObject_GetAttr(cls, k_extensions_by_name));
-  if (extensions_by_name == NULL) {
-    PyErr_SetString(PyExc_TypeError, "no extensions_by_name on class");
+  if (!PyObject_TypeCheck(cls, &CMessageClass_Type)) {
+    PyErr_Format(PyExc_TypeError, "Expected a message class, got %s",
+                 cls->ob_type->tp_name);
     return NULL;
   }
-  ScopedPyObjectPtr full_name(PyObject_GetAttr(extension_handle, kfull_name));
-  if (full_name == NULL) {
+  CMessageClass *message_class = reinterpret_cast<CMessageClass*>(cls);
+  if (message_class == NULL) {
     return NULL;
   }
-
   // If the extension was already registered, check that it is the same.
-  PyObject* existing_extension =
-      PyDict_GetItem(extensions_by_name.get(), full_name.get());
-  if (existing_extension != NULL) {
-    const FieldDescriptor* existing_extension_descriptor =
-        GetExtensionDescriptor(existing_extension);
-    if (existing_extension_descriptor != descriptor) {
-      PyErr_SetString(PyExc_ValueError, "Double registration of Extensions");
-      return NULL;
-    }
-    // Nothing else to do.
-    Py_RETURN_NONE;
-  }
-
-  if (PyDict_SetItem(extensions_by_name.get(), full_name.get(),
-                     extension_handle) < 0) {
-    return NULL;
-  }
-
-  // Also store a mapping from extension number to implementing class.
-  ScopedPyObjectPtr extensions_by_number(
-      PyObject_GetAttr(cls, k_extensions_by_number));
-  if (extensions_by_number == NULL) {
-    PyErr_SetString(PyExc_TypeError, "no extensions_by_number on class");
-    return NULL;
-  }
-
-  ScopedPyObjectPtr number(PyObject_GetAttrString(extension_handle, "number"));
-  if (number == NULL) {
-    return NULL;
-  }
-
-  // If the extension was already registered by number, check that it is the
-  // same.
-  existing_extension = PyDict_GetItem(extensions_by_number.get(), number.get());
-  if (existing_extension != NULL) {
-    const FieldDescriptor* existing_extension_descriptor =
-        GetExtensionDescriptor(existing_extension);
-    if (existing_extension_descriptor != descriptor) {
-      const Descriptor* msg_desc = GetMessageDescriptor(
-          reinterpret_cast<PyTypeObject*>(cls));
-      PyErr_Format(
-          PyExc_ValueError,
-          "Extensions \"%s\" and \"%s\" both try to extend message type "
-          "\"%s\" with field number %ld.",
-          existing_extension_descriptor->full_name().c_str(),
-          descriptor->full_name().c_str(),
-          msg_desc->full_name().c_str(),
-          PyInt_AsLong(number.get()));
-      return NULL;
-    }
-    // Nothing else to do.
-    Py_RETURN_NONE;
-  }
-  if (PyDict_SetItem(extensions_by_number.get(), number.get(),
-                     extension_handle) < 0) {
+  const FieldDescriptor* existing_extension =
+      message_class->py_message_factory->pool->pool->FindExtensionByNumber(
+          descriptor->containing_type(), descriptor->number());
+  if (existing_extension != NULL && existing_extension != descriptor) {
+    PyErr_SetString(PyExc_ValueError, "Double registration of Extensions");
     return NULL;
   }
-
-  // Check if it's a message set
-  if (descriptor->is_extension() &&
-      descriptor->containing_type()->options().message_set_wire_format() &&
-      descriptor->type() == FieldDescriptor::TYPE_MESSAGE &&
-      descriptor->label() == FieldDescriptor::LABEL_OPTIONAL) {
-    ScopedPyObjectPtr message_name(PyString_FromStringAndSize(
-        descriptor->message_type()->full_name().c_str(),
-        descriptor->message_type()->full_name().size()));
-    if (message_name == NULL) {
-      return NULL;
-    }
-    PyDict_SetItem(extensions_by_name.get(), message_name.get(),
-                   extension_handle);
-  }
-
   Py_RETURN_NONE;
 }
 
@@ -2087,7 +2106,7 @@ static PyObject* WhichOneof(CMessage* self, PyObject* arg) {
 static PyObject* GetExtensionDict(CMessage* self, void *closure);
 
 static PyObject* ListFields(CMessage* self) {
-  vector<const FieldDescriptor*> fields;
+  std::vector<const FieldDescriptor*> fields;
   self->message->GetReflection()->ListFields(*self->message, &fields);
 
   // Normally, the list will be exactly the size of the fields.
@@ -2178,7 +2197,7 @@ static PyObject* DiscardUnknownFields(CMessage* self) {
 
 PyObject* FindInitializationErrors(CMessage* self) {
   Message* message = self->message;
-  vector<string> errors;
+  std::vector<string> errors;
   message->FindInitializationErrors(&errors);
 
   PyObject* error_list = PyList_New(errors.size());
@@ -2570,11 +2589,24 @@ static PyObject* GetExtensionDict(CMessage* self, void *closure) {
   return NULL;
 }
 
+static PyObject* GetExtensionsByName(CMessage *self, void *closure) {
+  return message_meta::GetExtensionsByName(
+      reinterpret_cast<CMessageClass*>(Py_TYPE(self)), closure);
+}
+
+static PyObject* GetExtensionsByNumber(CMessage *self, void *closure) {
+  return message_meta::GetExtensionsByNumber(
+      reinterpret_cast<CMessageClass*>(Py_TYPE(self)), closure);
+}
+
 static PyGetSetDef Getters[] = {
   {"Extensions", (getter)GetExtensionDict, NULL, "Extension dict"},
+  {"_extensions_by_name", (getter)GetExtensionsByName, NULL},
+  {"_extensions_by_number", (getter)GetExtensionsByNumber, NULL},
   {NULL}
 };
 
+
 static PyMethodDef Methods[] = {
   { "__deepcopy__", (PyCFunction)DeepCopy, METH_VARARGS,
     "Makes a deep copy of the class." },
@@ -2835,19 +2867,7 @@ void InitGlobals() {
   // TODO(gps): Check all return values in this function for NULL and propagate
   // the error (MemoryError) on up to result in an import failure.  These should
   // also be freed and reset to NULL during finalization.
-  kPythonZero = PyInt_FromLong(0);
-  kint32min_py = PyInt_FromLong(kint32min);
-  kint32max_py = PyInt_FromLong(kint32max);
-  kuint32max_py = PyLong_FromLongLong(kuint32max);
-  kint64min_py = PyLong_FromLongLong(kint64min);
-  kint64max_py = PyLong_FromLongLong(kint64max);
-  kuint64max_py = PyLong_FromUnsignedLongLong(kuint64max);
-
   kDESCRIPTOR = PyString_FromString("DESCRIPTOR");
-  k_cdescriptor = PyString_FromString("_cdescriptor");
-  kfull_name = PyString_FromString("full_name");
-  k_extensions_by_name = PyString_FromString("_extensions_by_name");
-  k_extensions_by_number = PyString_FromString("_extensions_by_number");
 
   PyObject *dummy_obj = PySet_New(NULL);
   kEmptyWeakref = PyWeakref_NewRef(dummy_obj, NULL);
@@ -2887,25 +2907,6 @@ bool InitProto2MessageModule(PyObject *m) {
   // DESCRIPTOR is set on each protocol buffer message class elsewhere, but set
   // it here as well to document that subclasses need to set it.
   PyDict_SetItem(CMessage_Type.tp_dict, kDESCRIPTOR, Py_None);
-  // Subclasses with message extensions will override _extensions_by_name and
-  // _extensions_by_number with fresh mutable dictionaries in AddDescriptors.
-  // All other classes can share this same immutable mapping.
-  ScopedPyObjectPtr empty_dict(PyDict_New());
-  if (empty_dict == NULL) {
-    return false;
-  }
-  ScopedPyObjectPtr immutable_dict(PyDictProxy_New(empty_dict.get()));
-  if (immutable_dict == NULL) {
-    return false;
-  }
-  if (PyDict_SetItem(CMessage_Type.tp_dict,
-                     k_extensions_by_name, immutable_dict.get()) < 0) {
-    return false;
-  }
-  if (PyDict_SetItem(CMessage_Type.tp_dict,
-                     k_extensions_by_number, immutable_dict.get()) < 0) {
-    return false;
-  }
 
   PyModule_AddObject(m, "Message", reinterpret_cast<PyObject*>(&CMessage_Type));
 
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index 1550724c..ce80497e 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -117,6 +117,7 @@ typedef struct CMessage {
   PyObject* weakreflist;
 } CMessage;
 
+extern PyTypeObject CMessageClass_Type;
 extern PyTypeObject CMessage_Type;
 
 
@@ -235,6 +236,10 @@ int InitAttributes(CMessage* self, PyObject* args, PyObject* kwargs);
 
 PyObject* MergeFrom(CMessage* self, PyObject* arg);
 
+// This method does not do anything beyond checking that no other extension
+// has been registered with the same field number on this class.
+PyObject* RegisterExtension(PyObject* cls, PyObject* extension_handle);
+
 // Retrieves an attribute named 'name' from CMessage 'self'. Returns
 // the attribute value on success, or NULL on failure.
 //
@@ -275,25 +280,25 @@ PyObject* SetAllowOversizeProtos(PyObject* m, PyObject* arg);
 
 #define GOOGLE_CHECK_GET_INT32(arg, value, err)                        \
     int32 value;                                            \
-    if (!CheckAndGetInteger(arg, &value, kint32min_py, kint32max_py)) { \
+    if (!CheckAndGetInteger(arg, &value)) { \
       return err;                                          \
     }
 
 #define GOOGLE_CHECK_GET_INT64(arg, value, err)                        \
     int64 value;                                            \
-    if (!CheckAndGetInteger(arg, &value, kint64min_py, kint64max_py)) { \
+    if (!CheckAndGetInteger(arg, &value)) { \
       return err;                                          \
     }
 
 #define GOOGLE_CHECK_GET_UINT32(arg, value, err)                       \
     uint32 value;                                           \
-    if (!CheckAndGetInteger(arg, &value, kPythonZero, kuint32max_py)) { \
+    if (!CheckAndGetInteger(arg, &value)) { \
       return err;                                          \
     }
 
 #define GOOGLE_CHECK_GET_UINT64(arg, value, err)                       \
     uint64 value;                                           \
-    if (!CheckAndGetInteger(arg, &value, kPythonZero, kuint64max_py)) { \
+    if (!CheckAndGetInteger(arg, &value)) { \
       return err;                                          \
     }
 
@@ -316,20 +321,11 @@ PyObject* SetAllowOversizeProtos(PyObject* m, PyObject* arg);
     }
 
 
-extern PyObject* kPythonZero;
-extern PyObject* kint32min_py;
-extern PyObject* kint32max_py;
-extern PyObject* kuint32max_py;
-extern PyObject* kint64min_py;
-extern PyObject* kint64max_py;
-extern PyObject* kuint64max_py;
-
 #define FULL_MODULE_NAME "google.protobuf.pyext._message"
 
 void FormatTypeError(PyObject* arg, char* expected_types);
 template<class T>
-bool CheckAndGetInteger(
-    PyObject* arg, T* value, PyObject* min, PyObject* max);
+bool CheckAndGetInteger(PyObject* arg, T* value);
 bool CheckAndGetDouble(PyObject* arg, double* value);
 bool CheckAndGetFloat(PyObject* arg, float* value);
 bool CheckAndGetBool(PyObject* arg, bool* value);
diff --git a/python/google/protobuf/pyext/message_factory.cc b/python/google/protobuf/pyext/message_factory.cc
index 2ad89022..e0b45bf2 100644
--- a/python/google/protobuf/pyext/message_factory.cc
+++ b/python/google/protobuf/pyext/message_factory.cc
@@ -130,6 +130,72 @@ int RegisterMessageClass(PyMessageFactory* self,
   return 0;
 }
 
+CMessageClass* GetOrCreateMessageClass(PyMessageFactory* self,
+                                       const Descriptor* descriptor) {
+  // This is the same implementation as MessageFactory.GetPrototype().
+  ScopedPyObjectPtr py_descriptor(
+      PyMessageDescriptor_FromDescriptor(descriptor));
+  if (py_descriptor == NULL) {
+    return NULL;
+  }
+  // Do not create a MessageClass that already exists.
+  hash_map<const Descriptor*, CMessageClass*>::iterator it =
+      self->classes_by_descriptor->find(descriptor);
+  if (it != self->classes_by_descriptor->end()) {
+    Py_INCREF(it->second);
+    return it->second;
+  }
+  // Create a new message class.
+  ScopedPyObjectPtr args(Py_BuildValue(
+      "s(){sOsOsO}", descriptor->name().c_str(),
+      "DESCRIPTOR", py_descriptor.get(),
+      "__module__", Py_None,
+      "message_factory", self));
+  if (args == NULL) {
+    return NULL;
+  }
+  ScopedPyObjectPtr message_class(PyObject_CallObject(
+      reinterpret_cast<PyObject*>(&CMessageClass_Type), args.get()));
+  if (message_class == NULL) {
+    return NULL;
+  }
+  // Create messages class for the messages used by the fields, and registers
+  // all extensions for these messages during the recursion.
+  for (int field_idx = 0; field_idx < descriptor->field_count(); field_idx++) {
+    const Descriptor* sub_descriptor =
+        descriptor->field(field_idx)->message_type();
+    // It is NULL if the field type is not a message.
+    if (sub_descriptor != NULL) {
+      CMessageClass* result = GetOrCreateMessageClass(self, sub_descriptor);
+      if (result == NULL) {
+        return NULL;
+      }
+      Py_DECREF(result);
+    }
+  }
+
+  // Register extensions defined in this message.
+  for (int ext_idx = 0 ; ext_idx < descriptor->extension_count() ; ext_idx++) {
+    const FieldDescriptor* extension = descriptor->extension(ext_idx);
+    ScopedPyObjectPtr py_extended_class(
+        GetOrCreateMessageClass(self, extension->containing_type())
+            ->AsPyObject());
+    if (py_extended_class == NULL) {
+      return NULL;
+    }
+    ScopedPyObjectPtr py_extension(PyFieldDescriptor_FromDescriptor(extension));
+    if (py_extension == NULL) {
+      return NULL;
+    }
+    ScopedPyObjectPtr result(cmessage::RegisterExtension(
+        py_extended_class.get(), py_extension.get()));
+    if (result == NULL) {
+      return NULL;
+    }
+  }
+  return reinterpret_cast<CMessageClass*>(message_class.release());
+}
+
 // Retrieve the message class added to our database.
 CMessageClass* GetMessageClass(PyMessageFactory* self,
                                const Descriptor* message_descriptor) {
diff --git a/python/google/protobuf/pyext/message_factory.h b/python/google/protobuf/pyext/message_factory.h
index 07cccbfb..36092f7e 100644
--- a/python/google/protobuf/pyext/message_factory.h
+++ b/python/google/protobuf/pyext/message_factory.h
@@ -82,14 +82,14 @@ PyMessageFactory* NewMessageFactory(PyTypeObject* type, PyDescriptorPool* pool);
 int RegisterMessageClass(PyMessageFactory* self,
                          const Descriptor* message_descriptor,
                          CMessageClass* message_class);
-
-// Retrieves the Python class registered with the given message descriptor.
-//
-// Returns a *borrowed* reference if found, otherwise returns NULL with an
-// exception set.
+// Retrieves the Python class registered with the given message descriptor, or
+// fail with a TypeError. Returns a *borrowed* reference.
 CMessageClass* GetMessageClass(PyMessageFactory* self,
                                const Descriptor* message_descriptor);
-
+// Retrieves the Python class registered with the given message descriptor.
+// The class is created if not done yet. Returns a *new* reference.
+CMessageClass* GetOrCreateMessageClass(PyMessageFactory* self,
+                                       const Descriptor* message_descriptor);
 }  // namespace message_factory
 
 // Initialize objects used by this module.
diff --git a/python/google/protobuf/pyext/safe_numerics.h b/python/google/protobuf/pyext/safe_numerics.h
new file mode 100644
index 00000000..639ba2c8
--- /dev/null
+++ b/python/google/protobuf/pyext/safe_numerics.h
@@ -0,0 +1,164 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_PYTHON_CPP_SAFE_NUMERICS_H__
+#define GOOGLE_PROTOBUF_PYTHON_CPP_SAFE_NUMERICS_H__
+// Copied from chromium with only changes to the namespace.
+
+#include <limits>
+
+#include <google/protobuf/stubs/logging.h>
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+namespace python {
+
+template <bool SameSize, bool DestLarger,
+          bool DestIsSigned, bool SourceIsSigned>
+struct IsValidNumericCastImpl;
+
+#define BASE_NUMERIC_CAST_CASE_SPECIALIZATION(A, B, C, D, Code) \
+template <> struct IsValidNumericCastImpl<A, B, C, D> { \
+  template <class Source, class DestBounds> static inline bool Test( \
+      Source source, DestBounds min, DestBounds max) { \
+    return Code; \
+  } \
+}
+
+#define BASE_NUMERIC_CAST_CASE_SAME_SIZE(DestSigned, SourceSigned, Code) \
+  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
+      true, true, DestSigned, SourceSigned, Code); \
+  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
+      true, false, DestSigned, SourceSigned, Code)
+
+#define BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(DestSigned, SourceSigned, Code) \
+  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
+      false, false, DestSigned, SourceSigned, Code); \
+
+#define BASE_NUMERIC_CAST_CASE_DEST_LARGER(DestSigned, SourceSigned, Code) \
+  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
+      false, true, DestSigned, SourceSigned, Code); \
+
+// The three top level cases are:
+// - Same size
+// - Source larger
+// - Dest larger
+// And for each of those three cases, we handle the 4 different possibilities
+// of signed and unsigned. This gives 12 cases to handle, which we enumerate
+// below.
+//
+// The last argument in each of the macros is the actual comparison code. It
+// has three arguments available, source (the value), and min/max which are
+// the ranges of the destination.
+
+
+// These are the cases where both types have the same size.
+
+// Both signed.
+BASE_NUMERIC_CAST_CASE_SAME_SIZE(true, true, true);
+// Both unsigned.
+BASE_NUMERIC_CAST_CASE_SAME_SIZE(false, false, true);
+// Dest unsigned, Source signed.
+BASE_NUMERIC_CAST_CASE_SAME_SIZE(false, true, source >= 0);
+// Dest signed, Source unsigned.
+// This cast is OK because Dest's max must be less than Source's.
+BASE_NUMERIC_CAST_CASE_SAME_SIZE(true, false,
+                                 source <= static_cast<Source>(max));
+
+
+// These are the cases where Source is larger.
+
+// Both unsigned.
+BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(false, false, source <= max);
+// Both signed.
+BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(true, true,
+                                     source >= min && source <= max);
+// Dest is unsigned, Source is signed.
+BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(false, true,
+                                     source >= 0 && source <= max);
+// Dest is signed, Source is unsigned.
+// This cast is OK because Dest's max must be less than Source's.
+BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(true, false,
+                                     source <= static_cast<Source>(max));
+
+
+// These are the cases where Dest is larger.
+
+// Both unsigned.
+BASE_NUMERIC_CAST_CASE_DEST_LARGER(false, false, true);
+// Both signed.
+BASE_NUMERIC_CAST_CASE_DEST_LARGER(true, true, true);
+// Dest is unsigned, Source is signed.
+BASE_NUMERIC_CAST_CASE_DEST_LARGER(false, true, source >= 0);
+// Dest is signed, Source is unsigned.
+BASE_NUMERIC_CAST_CASE_DEST_LARGER(true, false, true);
+
+#undef BASE_NUMERIC_CAST_CASE_SPECIALIZATION
+#undef BASE_NUMERIC_CAST_CASE_SAME_SIZE
+#undef BASE_NUMERIC_CAST_CASE_SOURCE_LARGER
+#undef BASE_NUMERIC_CAST_CASE_DEST_LARGER
+
+
+// The main test for whether the conversion will under or overflow.
+template <class Dest, class Source>
+inline bool IsValidNumericCast(Source source) {
+  typedef std::numeric_limits<Source> SourceLimits;
+  typedef std::numeric_limits<Dest> DestLimits;
+  GOOGLE_COMPILE_ASSERT(SourceLimits::is_specialized, argument_must_be_numeric);
+  GOOGLE_COMPILE_ASSERT(SourceLimits::is_integer, argument_must_be_integral);
+  GOOGLE_COMPILE_ASSERT(DestLimits::is_specialized, result_must_be_numeric);
+  GOOGLE_COMPILE_ASSERT(DestLimits::is_integer, result_must_be_integral);
+
+  return IsValidNumericCastImpl<
+      sizeof(Dest) == sizeof(Source),
+      (sizeof(Dest) > sizeof(Source)),
+      DestLimits::is_signed,
+      SourceLimits::is_signed>::Test(
+          source,
+          DestLimits::min(),
+          DestLimits::max());
+}
+
+// checked_numeric_cast<> is analogous to static_cast<> for numeric types,
+// except that it CHECKs that the specified numeric conversion will not
+// overflow or underflow. Floating point arguments are not currently allowed
+// (this is COMPILE_ASSERTd), though this could be supported if necessary.
+template <class Dest, class Source>
+inline Dest checked_numeric_cast(Source source) {
+  GOOGLE_CHECK(IsValidNumericCast<Dest>(source));
+  return static_cast<Dest>(source);
+}
+
+}  // namespace python
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_PYTHON_CPP_SAFE_NUMERICS_H__