9 files changed, 155 insertions, 14 deletions
diff --git a/python/README.md b/python/README.md
index 4c194297..4b48225a 100644
--- a/python/README.md
+++ b/python/README.md
@@ -30,7 +30,7 @@ join the Protocol Buffers discussion list and let us know!
 Installation
 ============
 
-1) Make sure you have Python 2.6 or newer.  If in doubt, run:
+1) Make sure you have Python 2.7 or newer.  If in doubt, run:
 
        $ python -V
 
diff --git a/python/google/protobuf/internal/json_format_test.py b/python/google/protobuf/internal/json_format_test.py
index d891dce1..7f649406 100644
--- a/python/google/protobuf/internal/json_format_test.py
+++ b/python/google/protobuf/internal/json_format_test.py
@@ -791,9 +791,6 @@ class JsonFormatTest(JsonFormatBase):
     json_format.Parse(text, parsed_message, ignore_unknown_fields=True)
 
   def testDuplicateField(self):
-    # Duplicate key check is not supported for python2.6
-    if sys.version_info < (2, 7):
-      return
     self.CheckError('{"int32Value": 1,\n"int32Value":2}',
                     'Failed to load JSON: duplicate key int32Value.')
 
diff --git a/python/google/protobuf/json_format.py b/python/google/protobuf/json_format.py
index 8d338d3e..58c94a47 100644
--- a/python/google/protobuf/json_format.py
+++ b/python/google/protobuf/json_format.py
@@ -396,11 +396,7 @@ def Parse(text, message, ignore_unknown_fields=False):
   """
   if not isinstance(text, six.text_type): text = text.decode('utf-8')
   try:
-    if sys.version_info < (2, 7):
-      # object_pair_hook is not supported before python2.7
-      js = json.loads(text)
-    else:
-      js = json.loads(text, object_pairs_hook=_DuplicateChecker)
+    js = json.loads(text, object_pairs_hook=_DuplicateChecker)
   except ValueError as e:
     raise ParseError('Failed to load JSON: {0}.'.format(str(e)))
   return ParseDict(js, message, ignore_unknown_fields)
diff --git a/python/google/protobuf/proto_api.h b/python/google/protobuf/proto_api.h
new file mode 100644
index 00000000..5c076d23
--- /dev/null
+++ b/python/google/protobuf/proto_api.h
@@ -0,0 +1,92 @@
+// 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.
+
+// This file can be included by other C++ libraries, typically extension modules
+// which want to interact with the Python Messages coming from the "cpp"
+// implementation of protocol buffers.
+//
+// Usage:
+// Declare a (probably static) variable to hold the API:
+//    const PyProto_API* py_proto_api;
+// In some initialization function, write:
+//    py_proto_api = static_cast<const PyProto_API*>(PyCapsule_Import(
+//        PyProtoAPICapsuleName(), 0));
+//    if (!py_proto_api) { ...handle ImportError... }
+// Then use the methods of the returned class:
+//    py_proto_api->GetMessagePointer(...);
+
+#ifndef PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
+#define PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
+
+#include <Python.h>
+
+namespace google {
+namespace protobuf {
+
+class Message;
+
+namespace python {
+
+// Note on the implementation:
+// This API is designed after
+// https://docs.python.org/3/extending/extending.html#providing-a-c-api-for-an-extension-module
+// The class below contains no mutable state, and all methods are "const";
+// we use a C++ class instead of a C struct with functions pointers just because
+// the code looks more readable.
+struct PyProto_API {
+  // The API object is created at initialization time and never freed.
+  // This destructor is never called.
+  virtual ~PyProto_API() {}
+
+  // Operations on Messages.
+
+  // If the passed object is a Python Message, returns its internal pointer.
+  // Otherwise, returns NULL with an exception set.
+  virtual const Message* GetMessagePointer(PyObject* msg) const = 0;
+
+  // If the passed object is a Python Message, returns a mutable pointer.
+  // Otherwise, returns NULL with an exception set.
+  // This function will succeed only if there are no other Python objects
+  // pointing to the message, like submessages or repeated containers.
+  // With the current implementation, only empty messages are in this case.
+  virtual Message* GetMutableMessagePointer(PyObject* msg) const = 0;
+};
+
+inline const char* PyProtoAPICapsuleName() {
+  static const char kCapsuleName[] =
+      "google.protobuf.pyext._message.proto_API";
+  return kCapsuleName;
+}
+
+}  // namespace python
+}  // namespace protobuf
+}  // namespace google
+
+#endif  // PYTHON_GOOGLE_PROTOBUF_PROTO_API_H__
diff --git a/python/google/protobuf/pyext/message.cc b/python/google/protobuf/pyext/message.cc
index 5893533a..53736b9c 100644
--- a/python/google/protobuf/pyext/message.cc
+++ b/python/google/protobuf/pyext/message.cc
@@ -2866,17 +2866,38 @@ const Message* (*GetCProtoInsidePyProtoPtr)(PyObject* msg);
 Message* (*MutableCProtoInsidePyProtoPtr)(PyObject* msg);
 
 static const Message* GetCProtoInsidePyProtoImpl(PyObject* msg) {
+  const Message* message = PyMessage_GetMessagePointer(msg);
+  if (message == NULL) {
+    PyErr_Clear();
+    return NULL;
+  }
+  return message;
+}
+
+static Message* MutableCProtoInsidePyProtoImpl(PyObject* msg) {
+  Message* message = PyMessage_GetMutableMessagePointer(msg);
+  if (message == NULL) {
+    PyErr_Clear();
+    return NULL;
+  }
+  return message;
+}
+
+const Message* PyMessage_GetMessagePointer(PyObject* msg) {
   if (!PyObject_TypeCheck(msg, &CMessage_Type)) {
+    PyErr_SetString(PyExc_TypeError, "Not a Message instance");
     return NULL;
   }
   CMessage* cmsg = reinterpret_cast<CMessage*>(msg);
   return cmsg->message;
 }
 
-static Message* MutableCProtoInsidePyProtoImpl(PyObject* msg) {
+Message* PyMessage_GetMutableMessagePointer(PyObject* msg) {
   if (!PyObject_TypeCheck(msg, &CMessage_Type)) {
+    PyErr_SetString(PyExc_TypeError, "Not a Message instance");
     return NULL;
   }
+
   CMessage* cmsg = reinterpret_cast<CMessage*>(msg);
   if ((cmsg->composite_fields && PyDict_Size(cmsg->composite_fields) != 0) ||
       (cmsg->extensions != NULL &&
@@ -2885,6 +2906,9 @@ static Message* MutableCProtoInsidePyProtoImpl(PyObject* msg) {
     // the underlying C++ message back to the CMessage (e.g. removed repeated
     // composite containers). We only allow direct mutation of the underlying
     // C++ message if there is no child data in the CMessage.
+    PyErr_SetString(PyExc_ValueError,
+                    "Cannot reliably get a mutable pointer "
+                    "to a message with extra references");
     return NULL;
   }
   cmessage::AssureWritable(cmsg);
diff --git a/python/google/protobuf/pyext/message.h b/python/google/protobuf/pyext/message.h
index 72bcfa83..d754e62a 100644
--- a/python/google/protobuf/pyext/message.h
+++ b/python/google/protobuf/pyext/message.h
@@ -341,6 +341,9 @@ bool CheckFieldBelongsToMessage(const FieldDescriptor* field_descriptor,
 
 extern PyObject* PickleError_class;
 
+const Message* PyMessage_GetMessagePointer(PyObject* msg);
+Message* PyMessage_GetMutableMessagePointer(PyObject* msg);
+
 bool InitProto2MessageModule(PyObject *m);
 
 #if LANG_CXX11
diff --git a/python/google/protobuf/pyext/message_module.cc b/python/google/protobuf/pyext/message_module.cc
index 7c4df47f..8c933866 100644
--- a/python/google/protobuf/pyext/message_module.cc
+++ b/python/google/protobuf/pyext/message_module.cc
@@ -31,9 +31,26 @@
 #include <Python.h>
 
 #include <google/protobuf/pyext/message.h>
+#include <google/protobuf/proto_api.h>
 
 #include <google/protobuf/message_lite.h>
 
+namespace {
+
+// C++ API.  Clients get at this via proto_api.h
+struct ApiImplementation : google::protobuf::python::PyProto_API {
+  const google::protobuf::Message*
+      GetMessagePointer(PyObject* msg) const override {
+    return google::protobuf::python::PyMessage_GetMessagePointer(msg);
+  }
+  google::protobuf::Message*
+      GetMutableMessagePointer(PyObject* msg) const override {
+    return google::protobuf::python::PyMessage_GetMutableMessagePointer(msg);
+  }
+};
+
+}  // namespace
+
 static PyObject* GetPythonProto3PreserveUnknownsDefault(
     PyObject* /*m*/, PyObject* /*args*/) {
   if (google::protobuf::internal::GetProto3PreserveUnknownsDefault()) {
@@ -113,6 +130,15 @@ extern "C" {
       Py_DECREF(m);
       return INITFUNC_ERRORVAL;
     }
+    
+    // Adds the C++ API
+    if (PyObject* api =
+            PyCapsule_New(new ApiImplementation(),
+                          google::protobuf::python::PyProtoAPICapsuleName(), NULL)) {
+      PyModule_AddObject(m, "proto_API", api);
+    } else {
+      return INITFUNC_ERRORVAL;
+    }
 
 #if PY_MAJOR_VERSION >= 3
     return m;
diff --git a/python/setup.py b/python/setup.py
index a9df075e..335e9114 100755
--- a/python/setup.py
+++ b/python/setup.py
@@ -44,6 +44,7 @@ def GetVersion():
 
   with open(os.path.join('google', 'protobuf', '__init__.py')) as version_file:
     exec(version_file.read(), globals())
+    global __version__
     return __version__
 
 
@@ -148,10 +149,9 @@ class build_py(_build_py):
 class test_conformance(_build_py):
   target = 'test_python'
   def run(self):
-    if sys.version_info >= (2, 7):
-      # Python 2.6 dodges these extra failures.
-      os.environ["CONFORMANCE_PYTHON_EXTRA_FAILURES"] = (
-          "--failure_list failure_list_python-post26.txt")
+    # Python 2.6 dodges these extra failures.
+    os.environ["CONFORMANCE_PYTHON_EXTRA_FAILURES"] = (
+        "--failure_list failure_list_python-post26.txt")
     cmd = 'cd ../conformance && make %s' % (test_conformance.target)
     status = subprocess.check_call(cmd, shell=True)
 
diff --git a/python/stubout.py b/python/stubout.py
index aee4f2da..ba391045 100755
--- a/python/stubout.py
+++ b/python/stubout.py
@@ -17,6 +17,9 @@
 # This file is used for testing.  The original is at:
 #   http://code.google.com/p/pymox/
 
+import inspect
+
+
 class StubOutForTesting:
   """Sample Usage:
      You want os.path.exists() to always return true during testing.