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

# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.  All rights reserved.
# https://developers.google.com/protocol-buffers/
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"""Determine which implementation of the protobuf API is used in this process.
"""

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')

# 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.
_implementation_type = os.getenv('PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION',
                                 _default_implementation_type)

if _implementation_type != 'python':
  _implementation_type = 'cpp'

# 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.
_implementation_version_str = os.getenv(
    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION', '2')

if _implementation_version_str != '2':
  raise ValueError(
      'unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: "' +
      _implementation_version_str + '" (supported versions: 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.
# Please don't use this function if possible.
def Type():
  return _implementation_type


# See comment on 'Type' above.
def Version():
  return _implementation_version