Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/python/google/protobuf/internal/api_implementation.py

Index: third_party/protobuf/python/google/protobuf/internal/api_implementation.py
diff --git a/third_party/protobuf/python/google/protobuf/internal/api_implementation.py b/third_party/protobuf/python/google/protobuf/internal/api_implementation.py
index ffcf751167a5a973fa2e48f06a7b2920802fa494..ce02a32924c48c02d52427ed931deb27c855d28b 100644
--- a/third_party/protobuf/python/google/protobuf/internal/api_implementation.py
+++ b/third_party/protobuf/python/google/protobuf/internal/api_implementation.py
@@ -1,6 +1,6 @@
 # Protocol Buffers - Google's data interchange format
 # Copyright 2008 Google Inc.  All rights reserved.
-# https://developers.google.com/protocol-buffers/
+# http://code.google.com/p/protobuf/
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
@@ -28,72 +28,53 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-"""Determine which implementation of the protobuf API is used in this process.
+"""
+This module is the central entity that determines which implementation of the
+API is used.
 """
 
-import os
-import sys
-
-try:
-  # pylint: disable=g-import-not-at-top
-  from google.protobuf.internal import _api_implementation
-  # The compile-time constants in the _api_implementation module can be used to
-  # switch to a certain implementation of the Python API at build time.
-  _api_version = _api_implementation.api_version
-  _proto_extension_modules_exist_in_build = True
-except ImportError:
-  _api_version = -1  # Unspecified by compiler flags.
-  _proto_extension_modules_exist_in_build = False
-
-if _api_version == 1:
-  raise ValueError('api_version=1 is no longer supported.')
-if _api_version < 0:  # Still unspecified?
-  try:
-    # The presence of this module in a build allows the proto implementation to
-    # be upgraded merely via build deps rather than a compiler flag or the
-    # runtime environment variable.
-    # pylint: disable=g-import-not-at-top
-    from google.protobuf import _use_fast_cpp_protos
-    # Work around a known issue in the classic bootstrap .par import hook.
-    if not _use_fast_cpp_protos:
-      raise ImportError('_use_fast_cpp_protos import succeeded but was None')
-    del _use_fast_cpp_protos
-    _api_version = 2
-  except ImportError:
-    if _proto_extension_modules_exist_in_build:
-      if sys.version_info[0] >= 3:  # Python 3 defaults to C++ impl v2.
-        _api_version = 2
-      # TODO(b/17427486): Make Python 2 default to C++ impl v2.
-
-_default_implementation_type = (
-    'python' if _api_version <= 0 else 'cpp')
+__author__ = 'petar@google.com (Petar Petrov)'
 
+import os
 # This environment variable can be used to switch to a certain implementation
-# of the Python API, overriding the compile-time constants in the
-# _api_implementation module. Right now only 'python' and 'cpp' are valid
-# values. Any other value will be ignored.
+# of the Python API. Right now only 'python' and 'cpp' are valid values. Any
+# other value will be ignored.
 _implementation_type = os.getenv('PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION',
-                                 _default_implementation_type)
+                                 'python')
+
 
 if _implementation_type != 'python':
+  # For now, by default use the pure-Python implementation.
+  # The code below checks if the C extension is available and
+  # uses it if it is available.
   _implementation_type = 'cpp'
+  ## Determine automatically which implementation to use.
+  #try:
+  #  from google.protobuf.internal import cpp_message
+  #  _implementation_type = 'cpp'
+  #except ImportError, e:
+  #  _implementation_type = 'python'
+
 
 # This environment variable can be used to switch between the two
-# 'cpp' implementations, overriding the compile-time constants in the
-# _api_implementation module. Right now only '2' is supported. Any other
-# value will cause an error to be raised.
+# 'cpp' implementations. Right now only 1 and 2 are valid values. Any
+# other value will be ignored.
 _implementation_version_str = os.getenv(
-    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION', '2')
+    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION',
+    '1')
+
 
-if _implementation_version_str != '2':
+if _implementation_version_str not in ('1', '2'):
   raise ValueError(
-      'unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: "' +
-      _implementation_version_str + '" (supported versions: 2)'
+      "unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: '" +
+      _implementation_version_str + "' (supported versions: 1, 2)"
       )
 
+
 _implementation_version = int(_implementation_version_str)
 
 
+
 # Usage of this function is discouraged. Clients shouldn't care which
 # implementation of the API is in use. Note that there is no guarantee
 # that differences between APIs will be maintained.
@@ -101,7 +82,6 @@ _implementation_version = int(_implementation_version_str)
 def Type():
   return _implementation_type
 
-
 # See comment on 'Type' above.
 def Version():
   return _implementation_version