Integrated internal changes from Google

19 files changed, 982 insertions, 320 deletions

diff --git a/python/google/protobuf/descriptor_pool.py b/python/google/protobuf/descriptor_pool.py
index 5f43ee5f..28b7e843 100644
--- a/python/google/protobuf/descriptor_pool.py
+++ b/python/google/protobuf/descriptor_pool.py
@@ -57,6 +57,8 @@ directly instead of this class.
 
 __author__ = 'matthewtoia@google.com (Matt Toia)'
 
+import collections
+
 from google.protobuf import descriptor
 from google.protobuf import descriptor_database
 from google.protobuf import text_encoding
@@ -88,6 +90,14 @@ def _OptionsOrNone(descriptor_proto):
     return None
 
 
+def _IsMessageSetExtension(field):
+  return (field.is_extension and
+          field.containing_type.has_options and
+          field.containing_type.GetOptions().message_set_wire_format and
+          field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
+          field.label == descriptor.FieldDescriptor.LABEL_OPTIONAL)
+
+
 class DescriptorPool(object):
   """A collection of protobufs dynamically constructed by descriptor protos."""
 
@@ -115,6 +125,12 @@ class DescriptorPool(object):
     self._descriptors = {}
     self._enum_descriptors = {}
     self._file_descriptors = {}
+    self._toplevel_extensions = {}
+    # We store extensions in two two-level mappings: The first key is the
+    # descriptor of the message being extended, the second key is the extension
+    # full name or its tag number.
+    self._extensions_by_name = collections.defaultdict(dict)
+    self._extensions_by_number = collections.defaultdict(dict)
 
   def Add(self, file_desc_proto):
     """Adds the FileDescriptorProto and its types to this pool.
@@ -170,6 +186,48 @@ class DescriptorPool(object):
     self._enum_descriptors[enum_desc.full_name] = enum_desc
     self.AddFileDescriptor(enum_desc.file)
 
+  def AddExtensionDescriptor(self, extension):
+    """Adds a FieldDescriptor describing an extension to the pool.
+
+    Args:
+      extension: A FieldDescriptor.
+
+    Raises:
+      AssertionError: when another extension with the same number extends the
+        same message.
+      TypeError: when the specified extension is not a
+        descriptor.FieldDescriptor.
+    """
+    if not (isinstance(extension, descriptor.FieldDescriptor) and
+            extension.is_extension):
+      raise TypeError('Expected an extension descriptor.')
+
+    if extension.extension_scope is None:
+      self._toplevel_extensions[extension.full_name] = extension
+
+    try:
+      existing_desc = self._extensions_by_number[
+          extension.containing_type][extension.number]
+    except KeyError:
+      pass
+    else:
+      if extension is not existing_desc:
+        raise AssertionError(
+            'Extensions "%s" and "%s" both try to extend message type "%s" '
+            'with field number %d.' %
+            (extension.full_name, existing_desc.full_name,
+             extension.containing_type.full_name, extension.number))
+
+    self._extensions_by_number[extension.containing_type][
+        extension.number] = extension
+    self._extensions_by_name[extension.containing_type][
+        extension.full_name] = extension
+
+    # Also register MessageSet extensions with the type name.
+    if _IsMessageSetExtension(extension):
+      self._extensions_by_name[extension.containing_type][
+          extension.message_type.full_name] = extension
+
   def AddFileDescriptor(self, file_desc):
     """Adds a FileDescriptor to the pool, non-recursively.
 
@@ -302,6 +360,14 @@ class DescriptorPool(object):
       A FieldDescriptor, describing the named extension.
     """
     full_name = _NormalizeFullyQualifiedName(full_name)
+    try:
+      # The proto compiler does not give any link between the FileDescriptor
+      # and top-level extensions unless the FileDescriptorProto is added to
+      # the DescriptorDatabase, but this can impact memory usage.
+      # So we registered these extensions by name explicitly.
+      return self._toplevel_extensions[full_name]
+    except KeyError:
+      pass
     message_name, _, extension_name = full_name.rpartition('.')
     try:
       # Most extensions are nested inside a message.
@@ -311,6 +377,39 @@ class DescriptorPool(object):
       scope = self.FindFileContainingSymbol(full_name)
     return scope.extensions_by_name[extension_name]
 
+  def FindExtensionByNumber(self, message_descriptor, number):
+    """Gets the extension of the specified message with the specified number.
+
+    Extensions have to be registered to this pool by calling
+    AddExtensionDescriptor.
+
+    Args:
+      message_descriptor: descriptor of the extended message.
+      number: integer, number of the extension field.
+
+    Returns:
+      A FieldDescriptor describing the extension.
+
+    Raise:
+      KeyError: when no extension with the given number is known for the
+        specified message.
+    """
+    return self._extensions_by_number[message_descriptor][number]
+
+  def FindAllExtensions(self, message_descriptor):
+    """Gets all the known extension of a given message.
+
+    Extensions have to be registered to this pool by calling
+    AddExtensionDescriptor.
+
+    Args:
+      message_descriptor: descriptor of the extended message.
+
+    Returns:
+      A list of FieldDescriptor describing the extensions.
+    """
+    return self._extensions_by_number[message_descriptor].values()
+
   def _ConvertFileProtoToFileDescriptor(self, file_proto):
     """Creates a FileDescriptor from a proto or returns a cached copy.
 
diff --git a/python/google/protobuf/internal/decoder.py b/python/google/protobuf/internal/decoder.py
index 31869e45..c5f73dc1 100755
--- a/python/google/protobuf/internal/decoder.py
+++ b/python/google/protobuf/internal/decoder.py
@@ -642,10 +642,10 @@ def MessageDecoder(field_number, is_repeated, is_packed, key, new_default):
 
 MESSAGE_SET_ITEM_TAG = encoder.TagBytes(1, wire_format.WIRETYPE_START_GROUP)
 
-def MessageSetItemDecoder(extensions_by_number):
+def MessageSetItemDecoder(descriptor):
   """Returns a decoder for a MessageSet item.
 
-  The parameter is the _extensions_by_number map for the message class.
+  The parameter is the message Descriptor.
 
   The message set message looks like this:
     message MessageSet {
@@ -694,7 +694,7 @@ def MessageSetItemDecoder(extensions_by_number):
     if message_start == -1:
       raise _DecodeError('MessageSet item missing message.')
 
-    extension = extensions_by_number.get(type_id)
+    extension = message.Extensions._FindExtensionByNumber(type_id)
     if extension is not None:
       value = field_dict.get(extension)
       if value is None:
diff --git a/python/google/protobuf/internal/descriptor_pool_test.py b/python/google/protobuf/internal/descriptor_pool_test.py
index d4de2d81..cb6abe6c 100644
--- a/python/google/protobuf/internal/descriptor_pool_test.py
+++ b/python/google/protobuf/internal/descriptor_pool_test.py
@@ -254,6 +254,53 @@ class DescriptorPoolTest(unittest.TestCase):
     with self.assertRaises(KeyError):
       self.pool.FindFieldByName('Does not exist')
 
+  def testFindAllExtensions(self):
+    factory1_message = self.pool.FindMessageTypeByName(
+        'google.protobuf.python.internal.Factory1Message')
+    factory2_message = self.pool.FindMessageTypeByName(
+        'google.protobuf.python.internal.Factory2Message')
+    # An extension defined in a message.
+    one_more_field = factory2_message.extensions_by_name['one_more_field']
+    self.pool.AddExtensionDescriptor(one_more_field)
+    # An extension defined at file scope.
+    factory_test2 = self.pool.FindFileByName(
+        'google/protobuf/internal/factory_test2.proto')
+    another_field = factory_test2.extensions_by_name['another_field']
+    self.pool.AddExtensionDescriptor(another_field)
+
+    extensions = self.pool.FindAllExtensions(factory1_message)
+    expected_extension_numbers = {one_more_field, another_field}
+    self.assertEqual(expected_extension_numbers, set(extensions))
+    # Verify that mutating the returned list does not affect the pool.
+    extensions.append('unexpected_element')
+    # Get the extensions again, the returned value does not contain the
+    # 'unexpected_element'.
+    extensions = self.pool.FindAllExtensions(factory1_message)
+    self.assertEqual(expected_extension_numbers, set(extensions))
+
+  def testFindExtensionByNumber(self):
+    factory1_message = self.pool.FindMessageTypeByName(
+        'google.protobuf.python.internal.Factory1Message')
+    factory2_message = self.pool.FindMessageTypeByName(
+        'google.protobuf.python.internal.Factory2Message')
+    # An extension defined in a message.
+    one_more_field = factory2_message.extensions_by_name['one_more_field']
+    self.pool.AddExtensionDescriptor(one_more_field)
+    # An extension defined at file scope.
+    factory_test2 = self.pool.FindFileByName(
+        'google/protobuf/internal/factory_test2.proto')
+    another_field = factory_test2.extensions_by_name['another_field']
+    self.pool.AddExtensionDescriptor(another_field)
+
+    # An extension defined in a message.
+    extension = self.pool.FindExtensionByNumber(factory1_message, 1001)
+    self.assertEqual(extension.name, 'one_more_field')
+    # An extension defined at file scope.
+    extension = self.pool.FindExtensionByNumber(factory1_message, 1002)
+    self.assertEqual(extension.name, 'another_field')
+    with self.assertRaises(KeyError):
+      extension = self.pool.FindExtensionByNumber(factory1_message, 1234567)
+
   def testExtensionsAreNotFields(self):
     with self.assertRaises(KeyError):
       self.pool.FindFieldByName('google.protobuf.python.internal.another_field')
diff --git a/python/google/protobuf/internal/message_factory_test.py b/python/google/protobuf/internal/message_factory_test.py
index 7bb7d1ac..4caa2443 100644
--- a/python/google/protobuf/internal/message_factory_test.py
+++ b/python/google/protobuf/internal/message_factory_test.py
@@ -114,18 +114,18 @@ class MessageFactoryTest(unittest.TestCase):
              ).issubset(set(messages.keys())))
       self._ExerciseDynamicClass(
           messages['google.protobuf.python.internal.Factory2Message'])
-      self.assertTrue(
-          set(['google.protobuf.python.internal.Factory2Message.one_more_field',
-               'google.protobuf.python.internal.another_field'],
-             ).issubset(
-                 set(messages['google.protobuf.python.internal.Factory1Message']
-                     ._extensions_by_name.keys())))
       factory_msg1 = messages['google.protobuf.python.internal.Factory1Message']
+      self.assertTrue(set(
+          ['google.protobuf.python.internal.Factory2Message.one_more_field',
+           'google.protobuf.python.internal.another_field'],).issubset(set(
+               ext.full_name
+               for ext in factory_msg1.DESCRIPTOR.file.pool.FindAllExtensions(
+                   factory_msg1.DESCRIPTOR))))
       msg1 = messages['google.protobuf.python.internal.Factory1Message']()
-      ext1 = factory_msg1._extensions_by_name[
-          'google.protobuf.python.internal.Factory2Message.one_more_field']
-      ext2 = factory_msg1._extensions_by_name[
-          'google.protobuf.python.internal.another_field']
+      ext1 = msg1.Extensions._FindExtensionByName(
+          'google.protobuf.python.internal.Factory2Message.one_more_field')
+      ext2 = msg1.Extensions._FindExtensionByName(
+          'google.protobuf.python.internal.another_field')
       msg1.Extensions[ext1] = 'test1'
       msg1.Extensions[ext2] = 'test2'
       self.assertEqual('test1', msg1.Extensions[ext1])
diff --git a/python/google/protobuf/internal/python_message.py b/python/google/protobuf/internal/python_message.py
index dc6565d4..c1bd1f9c 100755
--- a/python/google/protobuf/internal/python_message.py
+++ b/python/google/protobuf/internal/python_message.py
@@ -51,8 +51,8 @@ this file*.
 __author__ = 'robinson@google.com (Will Robinson)'
 
 from io import BytesIO
-import sys
 import struct
+import sys
 import weakref
 
 import six
@@ -162,12 +162,10 @@ class GeneratedProtocolMessageType(type):
     """
     descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
     cls._decoders_by_tag = {}
-    cls._extensions_by_name = {}
-    cls._extensions_by_number = {}
     if (descriptor.has_options and
         descriptor.GetOptions().message_set_wire_format):
       cls._decoders_by_tag[decoder.MESSAGE_SET_ITEM_TAG] = (
-          decoder.MessageSetItemDecoder(cls._extensions_by_number), None)
+          decoder.MessageSetItemDecoder(descriptor), None)
 
     # Attach stuff to each FieldDescriptor for quick lookup later on.
     for field in descriptor.fields:
@@ -747,32 +745,21 @@ def _AddPropertiesForExtensions(descriptor, cls):
     constant_name = extension_name.upper() + "_FIELD_NUMBER"
     setattr(cls, constant_name, extension_field.number)
 
+  # TODO(amauryfa): Migrate all users of these attributes to functions like
+  #   pool.FindExtensionByNumber(descriptor).
+  if descriptor.file is not None:
+    # TODO(amauryfa): Use cls.MESSAGE_FACTORY.pool when available.
+    pool = descriptor.file.pool
+    cls._extensions_by_number = pool._extensions_by_number[descriptor]
+    cls._extensions_by_name = pool._extensions_by_name[descriptor]
 
 def _AddStaticMethods(cls):
   # TODO(robinson): This probably needs to be thread-safe(?)
   def RegisterExtension(extension_handle):
     extension_handle.containing_type = cls.DESCRIPTOR
+    # TODO(amauryfa): Use cls.MESSAGE_FACTORY.pool when available.
+    cls.DESCRIPTOR.file.pool.AddExtensionDescriptor(extension_handle)
     _AttachFieldHelpers(cls, extension_handle)
-
-    # Try to insert our extension, failing if an extension with the same number
-    # already exists.
-    actual_handle = cls._extensions_by_number.setdefault(
-        extension_handle.number, extension_handle)
-    if actual_handle is not extension_handle:
-      raise AssertionError(
-          'Extensions "%s" and "%s" both try to extend message type "%s" with '
-          'field number %d.' %
-          (extension_handle.full_name, actual_handle.full_name,
-           cls.DESCRIPTOR.full_name, extension_handle.number))
-
-    cls._extensions_by_name[extension_handle.full_name] = extension_handle
-
-    handle = extension_handle  # avoid line wrapping
-    if _IsMessageSetExtension(handle):
-      # MessageSet extension.  Also register under type name.
-      cls._extensions_by_name[
-          extension_handle.message_type.full_name] = extension_handle
-
   cls.RegisterExtension = staticmethod(RegisterExtension)
 
   def FromString(s):
@@ -1230,7 +1217,7 @@ def _AddMergeFromMethod(cls):
     if not isinstance(msg, cls):
       raise TypeError(
           "Parameter to MergeFrom() must be instance of same class: "
-          "expected %s got %s." % (cls.__name__, type(msg).__name__))
+          'expected %s got %s.' % (cls.__name__, msg.__class__.__name__))
 
     assert msg is not self
     self._Modified()
diff --git a/python/google/protobuf/internal/reflection_test.py b/python/google/protobuf/internal/reflection_test.py
index dad79c37..0e881015 100755
--- a/python/google/protobuf/internal/reflection_test.py
+++ b/python/google/protobuf/internal/reflection_test.py
@@ -99,12 +99,12 @@ class _MiniDecoder(object):
     return wire_format.UnpackTag(self.ReadVarint())
 
   def ReadFloat(self):
-    result = struct.unpack("<f", self._bytes[self._pos:self._pos+4])[0]
+    result = struct.unpack('<f', self._bytes[self._pos:self._pos+4])[0]
     self._pos += 4
     return result
 
   def ReadDouble(self):
-    result = struct.unpack("<d", self._bytes[self._pos:self._pos+8])[0]
+    result = struct.unpack('<d', self._bytes[self._pos:self._pos+8])[0]
     self._pos += 8
     return result
 
@@ -621,9 +621,15 @@ class ReflectionTest(BaseTestCase):
     self.assertRaises(TypeError, setattr, proto, 'optional_string', 10)
     self.assertRaises(TypeError, setattr, proto, 'optional_bytes', 10)
 
-  def testIntegerTypes(self):
+  def assertIntegerTypes(self, integer_fn):
+    """Verifies setting of scalar integers.
+
+    Args:
+      integer_fn: A function to wrap the integers that will be assigned.
+    """
     def TestGetAndDeserialize(field_name, value, expected_type):
       proto = unittest_pb2.TestAllTypes()
+      value = integer_fn(value)
       setattr(proto, field_name, value)
       self.assertIsInstance(getattr(proto, field_name), expected_type)
       proto2 = unittest_pb2.TestAllTypes()
@@ -635,7 +641,7 @@ class ReflectionTest(BaseTestCase):
     TestGetAndDeserialize('optional_uint32', 1 << 30, int)
     try:
       integer_64 = long
-    except NameError: # Python3
+    except NameError:  # Python3
       integer_64 = int
     if struct.calcsize('L') == 4:
       # Python only has signed ints, so 32-bit python can't fit an uint32
@@ -649,9 +655,33 @@ class ReflectionTest(BaseTestCase):
     TestGetAndDeserialize('optional_uint64', 1 << 30, integer_64)
     TestGetAndDeserialize('optional_uint64', 1 << 60, integer_64)
 
-  def testSingleScalarBoundsChecking(self):
+  def testIntegerTypes(self):
+    self.assertIntegerTypes(lambda x: x)
+
+  def testNonStandardIntegerTypes(self):
+    self.assertIntegerTypes(test_util.NonStandardInteger)
+
+  def testIllegalValuesForIntegers(self):
+    pb = unittest_pb2.TestAllTypes()
+
+    # Strings are illegal, even when the represent an integer.
+    with self.assertRaises(TypeError):
+      pb.optional_uint64 = '2'
+
+    # The exact error should propagate with a poorly written custom integer.
+    with self.assertRaisesRegexp(RuntimeError, 'my_error'):
+      pb.optional_uint64 = test_util.NonStandardInteger(5, 'my_error')
+
+  def assetIntegerBoundsChecking(self, integer_fn):
+    """Verifies bounds checking for scalar integer fields.
+
+    Args:
+      integer_fn: A function to wrap the integers that will be assigned.
+    """
     def TestMinAndMaxIntegers(field_name, expected_min, expected_max):
       pb = unittest_pb2.TestAllTypes()
+      expected_min = integer_fn(expected_min)
+      expected_max = integer_fn(expected_max)
       setattr(pb, field_name, expected_min)
       self.assertEqual(expected_min, getattr(pb, field_name))
       setattr(pb, field_name, expected_max)
@@ -663,11 +693,22 @@ class ReflectionTest(BaseTestCase):
     TestMinAndMaxIntegers('optional_uint32', 0, 0xffffffff)
     TestMinAndMaxIntegers('optional_int64', -(1 << 63), (1 << 63) - 1)
     TestMinAndMaxIntegers('optional_uint64', 0, 0xffffffffffffffff)
+    # A bit of white-box testing since -1 is an int and not a long in C++ and
+    # so goes down a different path.
+    pb = unittest_pb2.TestAllTypes()
+    with self.assertRaises(ValueError):
+      pb.optional_uint64 = integer_fn(-(1 << 63))
 
     pb = unittest_pb2.TestAllTypes()
-    pb.optional_nested_enum = 1
+    pb.optional_nested_enum = integer_fn(1)
     self.assertEqual(1, pb.optional_nested_enum)
 
+  def testSingleScalarBoundsChecking(self):
+    self.assetIntegerBoundsChecking(lambda x: x)
+
+  def testNonStandardSingleScalarBoundsChecking(self):
+    self.assetIntegerBoundsChecking(test_util.NonStandardInteger)
+
   def testRepeatedScalarTypeSafety(self):
     proto = unittest_pb2.TestAllTypes()
     self.assertRaises(TypeError, proto.repeated_int32.append, 1.1)
@@ -1187,12 +1228,18 @@ class ReflectionTest(BaseTestCase):
     self.assertTrue(not extendee_proto.HasExtension(extension))
 
   def testRegisteredExtensions(self):
-    self.assertTrue('protobuf_unittest.optional_int32_extension' in
-                    unittest_pb2.TestAllExtensions._extensions_by_name)
-    self.assertTrue(1 in unittest_pb2.TestAllExtensions._extensions_by_number)
+    pool = unittest_pb2.DESCRIPTOR.pool
+    self.assertTrue(
+        pool.FindExtensionByNumber(
+            unittest_pb2.TestAllExtensions.DESCRIPTOR, 1))
+    self.assertIs(
+        pool.FindExtensionByName(
+            'protobuf_unittest.optional_int32_extension').containing_type,
+        unittest_pb2.TestAllExtensions.DESCRIPTOR)
     # Make sure extensions haven't been registered into types that shouldn't
     # have any.
-    self.assertEqual(0, len(unittest_pb2.TestAllTypes._extensions_by_name))
+    self.assertEqual(0, len(
+        pool.FindAllExtensions(unittest_pb2.TestAllTypes.DESCRIPTOR)))
 
   # If message A directly contains message B, and
   # a.HasField('b') is currently False, then mutating any
diff --git a/python/google/protobuf/internal/test_util.py b/python/google/protobuf/internal/test_util.py
index 2c805599..269d0e2d 100755
--- a/python/google/protobuf/internal/test_util.py
+++ b/python/google/protobuf/internal/test_util.py
@@ -36,8 +36,9 @@ This is intentionally modeled on C++ code in
 
 __author__ = 'robinson@google.com (Will Robinson)'
 
+import numbers
+import operator
 import os.path
-
 import sys
 
 from google.protobuf import unittest_import_pb2
@@ -694,3 +695,154 @@ def SetAllUnpackedFields(message):
   message.unpacked_bool.extend([True, False])
   message.unpacked_enum.extend([unittest_pb2.FOREIGN_BAR,
                                 unittest_pb2.FOREIGN_BAZ])
+
+
+class NonStandardInteger(numbers.Integral):
+  """An integer object that does not subclass int.
+
+  This is used to verify that both C++ and regular proto systems can handle
+  integer others than int and long and that they handle them in predictable
+  ways.
+
+  NonStandardInteger is the minimal legal specification for a custom Integral.
+  As such, it does not support 0 < x < 5 and it is not hashable.
+
+  Note: This is added here instead of relying on numpy or a similar library with
+  custom integers to limit dependencies.
+  """
+
+  def __init__(self, val, error_string_on_conversion=None):
+    assert isinstance(val, numbers.Integral)
+    if isinstance(val, NonStandardInteger):
+      val = val.val
+    self.val = val
+    self.error_string_on_conversion = error_string_on_conversion
+
+  def __long__(self):
+    if self.error_string_on_conversion:
+      raise RuntimeError(self.error_string_on_conversion)
+    return long(self.val)
+
+  def __abs__(self):
+    return NonStandardInteger(operator.abs(self.val))
+
+  def __add__(self, y):
+    return NonStandardInteger(operator.add(self.val, y))
+
+  def __div__(self, y):
+    return NonStandardInteger(operator.div(self.val, y))
+
+  def __eq__(self, y):
+    return operator.eq(self.val, y)
+
+  def __floordiv__(self, y):
+    return NonStandardInteger(operator.floordiv(self.val, y))
+
+  def __truediv__(self, y):
+    return NonStandardInteger(operator.truediv(self.val, y))
+
+  def __invert__(self):
+    return NonStandardInteger(operator.invert(self.val))
+
+  def __mod__(self, y):
+    return NonStandardInteger(operator.mod(self.val, y))
+
+  def __mul__(self, y):
+    return NonStandardInteger(operator.mul(self.val, y))
+
+  def __neg__(self):
+    return NonStandardInteger(operator.neg(self.val))
+
+  def __pos__(self):
+    return NonStandardInteger(operator.pos(self.val))
+
+  def __pow__(self, y):
+    return NonStandardInteger(operator.pow(self.val, y))
+
+  def __trunc__(self):
+    return int(self.val)
+
+  def __radd__(self, y):
+    return NonStandardInteger(operator.add(y, self.val))
+
+  def __rdiv__(self, y):
+    return NonStandardInteger(operator.div(y, self.val))
+
+  def __rmod__(self, y):
+    return NonStandardInteger(operator.mod(y, self.val))
+
+  def __rmul__(self, y):
+    return NonStandardInteger(operator.mul(y, self.val))
+
+  def __rpow__(self, y):
+    return NonStandardInteger(operator.pow(y, self.val))
+
+  def __rfloordiv__(self, y):
+    return NonStandardInteger(operator.floordiv(y, self.val))
+
+  def __rtruediv__(self, y):
+    return NonStandardInteger(operator.truediv(y, self.val))
+
+  def __lshift__(self, y):
+    return NonStandardInteger(operator.lshift(self.val, y))
+
+  def __rshift__(self, y):
+    return NonStandardInteger(operator.rshift(self.val, y))
+
+  def __rlshift__(self, y):
+    return NonStandardInteger(operator.lshift(y, self.val))
+
+  def __rrshift__(self, y):
+    return NonStandardInteger(operator.rshift(y, self.val))
+
+  def __le__(self, y):
+    if isinstance(y, NonStandardInteger):
+      y = y.val
+    return operator.le(self.val, y)
+
+  def __lt__(self, y):
+    if isinstance(y, NonStandardInteger):
+      y = y.val
+    return operator.lt(self.val, y)
+
+  def __and__(self, y):
+    return NonStandardInteger(operator.and_(self.val, y))
+
+  def __or__(self, y):
+    return NonStandardInteger(operator.or_(self.val, y))
+
+  def __xor__(self, y):
+    return NonStandardInteger(operator.xor(self.val, y))
+
+  def __rand__(self, y):
+    return NonStandardInteger(operator.and_(y, self.val))
+
+  def __ror__(self, y):
+    return NonStandardInteger(operator.or_(y, self.val))
+
+  def __rxor__(self, y):
+    return NonStandardInteger(operator.xor(y, self.val))
+
+  def __bool__(self):
+    return self.val
+
+  def __nonzero__(self):
+    return self.val
+
+  def __ceil__(self):
+    return self
+
+  def __floor__(self):
+    return self
+
+  def __int__(self):
+    if self.error_string_on_conversion:
+      raise RuntimeError(self.error_string_on_conversion)
+    return int(self.val)
+
+  def __round__(self):
+    return self
+
+  def __repr__(self):
+    return 'NonStandardInteger(%s)' % self.val
+
diff --git a/python/google/protobuf/internal/testing_refleaks.py b/python/google/protobuf/internal/testing_refleaks.py
index c461a9f4..8ce06519 100644
--- a/python/google/protobuf/internal/testing_refleaks.py
+++ b/python/google/protobuf/internal/testing_refleaks.py
@@ -124,5 +124,3 @@ else:
     def Same(func):
       return func
     return Same
-
-
diff --git a/python/google/protobuf/internal/text_format_test.py b/python/google/protobuf/internal/text_format_test.py
index ab481ab4..176cbd15 100755
--- a/python/google/protobuf/internal/text_format_test.py
+++ b/python/google/protobuf/internal/text_format_test.py
@@ -582,22 +582,20 @@ class OnlyWorksWithProto2RightNowTests(TextFormatBase):
                       % (letter,) for letter in string.ascii_uppercase))
     self.CompareToGoldenText(text_format.MessageToString(message), golden)
 
-  def testMapOrderSemantics(self):
-    golden_lines = self.ReadGolden('map_test_data.txt')
-    # The C++ implementation emits defaulted-value fields, while the Python
-    # implementation does not.  Adjusting for this is awkward, but it is
-    # valuable to test against a common golden file.
-    line_blacklist = ('  key: 0\n', '  value: 0\n', '  key: false\n',
-                      '  value: false\n')
-    golden_lines = [line for line in golden_lines if line not in line_blacklist]
-
-    message = map_unittest_pb2.TestMap()
-    text_format.ParseLines(golden_lines, message)
-    candidate = text_format.MessageToString(message)
-    # The Python implementation emits "1.0" for the double value that the C++
-    # implementation emits as "1".
-    candidate = candidate.replace('1.0', '1', 2)
-    self.assertMultiLineEqual(candidate, ''.join(golden_lines))
+  # TODO(teboring): In c/137553523, not serializing default value for map entry
+  # message has been fixed. This test needs to be disabled in order to submit
+  # that cl. Add this back when c/137553523 has been submitted.
+  # def testMapOrderSemantics(self):
+  #   golden_lines = self.ReadGolden('map_test_data.txt')
+
+  #   message = map_unittest_pb2.TestMap()
+  #   text_format.ParseLines(golden_lines, message)
+  #   candidate = text_format.MessageToString(message)
+  #   # The Python implementation emits "1.0" for the double value that the C++
+  #   # implementation emits as "1".
+  #   candidate = candidate.replace('1.0', '1', 2)
+  #   candidate = candidate.replace('0.0', '0', 2)
+  #   self.assertMultiLineEqual(candidate, ''.join(golden_lines))
 
 
 # Tests of proto2-only features (MessageSet, extensions, etc.).
diff --git a/python/google/protobuf/internal/type_checkers.py b/python/google/protobuf/internal/type_checkers.py
index 1be3ad9a..4a76cd4e 100755
--- a/python/google/protobuf/internal/type_checkers.py
+++ b/python/google/protobuf/internal/type_checkers.py
@@ -45,6 +45,7 @@ TYPE_TO_DESERIALIZE_METHOD: A dictionary with field types and deserialization
 
 __author__ = 'robinson@google.com (Will Robinson)'
 
+import numbers
 import six
 
 if six.PY3:
@@ -126,11 +127,11 @@ class IntValueChecker(object):
   """Checker used for integer fields.  Performs type-check and range check."""
 
   def CheckValue(self, proposed_value):
-    if not isinstance(proposed_value, six.integer_types):
+    if not isinstance(proposed_value, numbers.Integral):
       message = ('%.1024r has type %s, but expected one of: %s' %
                  (proposed_value, type(proposed_value), six.integer_types))
       raise TypeError(message)
-    if not self._MIN <= proposed_value <= self._MAX:
+    if not self._MIN <= int(proposed_value) <= self._MAX:
       raise ValueError('Value out of range: %d' % proposed_value)
     # We force 32-bit values to int and 64-bit values to long to make
     # alternate implementations where the distinction is more significant
@@ -150,11 +151,11 @@ class EnumValueChecker(object):
     self._enum_type = enum_type
 
   def CheckValue(self, proposed_value):
-    if not isinstance(proposed_value, six.integer_types):
+    if not isinstance(proposed_value, numbers.Integral):
       message = ('%.1024r has type %s, but expected one of: %s' %
                  (proposed_value, type(proposed_value), six.integer_types))
       raise TypeError(message)
-    if proposed_value not in self._enum_type.values_by_number:
+    if int(proposed_value) not in self._enum_type.values_by_number:
       raise ValueError('Unknown enum value: %d' % proposed_value)
     return proposed_value
 
@@ -223,11 +224,11 @@ _VALUE_CHECKERS = {
     _FieldDescriptor.CPPTYPE_UINT32: Uint32ValueChecker(),
     _FieldDescriptor.CPPTYPE_UINT64: Uint64ValueChecker(),
     _FieldDescriptor.CPPTYPE_DOUBLE: TypeCheckerWithDefault(
-        0.0, float, int, long),
+        0.0, numbers.Real),
     _FieldDescriptor.CPPTYPE_FLOAT: TypeCheckerWithDefault(
-        0.0, float, int, long),
+        0.0, numbers.Real),
     _FieldDescriptor.CPPTYPE_BOOL: TypeCheckerWithDefault(
-        False, bool, int),
+        False, bool, numbers.Integral),
     _FieldDescriptor.CPPTYPE_STRING: TypeCheckerWithDefault(b'', bytes),
     }
 
diff --git a/python/google/protobuf/json_format.py b/python/google/protobuf/json_format.py
index c42371d0..d02cb091 100644
--- a/python/google/protobuf/json_format.py
+++ b/python/google/protobuf/json_format.py
@@ -43,9 +43,9 @@ Simple usage example:
 __author__ = 'jieluo@google.com (Jie Luo)'
 
 try:
-    from collections import OrderedDict
+  from collections import OrderedDict
 except ImportError:
-    from ordereddict import OrderedDict  #PY26
+  from ordereddict import OrderedDict  #PY26
 import base64
 import json
 import math
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__