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 warnings
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:
    try:
      # pylint: disable=g-import-not-at-top
      from google.protobuf.internal import use_pure_python
      del use_pure_python  # Avoids a pylint error and namespace pollution.
    except ImportError:
      # TODO(b/74017912): It's unsafe to enable :use_fast_cpp_protos by default;
      # it can cause data loss if you have any Python-only extensions to any
      # message passed back and forth with C++ code.
      #
      # TODO(b/17427486): Once that bug is fixed, we want to make both Python 2
      # and Python 3 default to `_api_version = 2` (C++ implementation V2).
      pass

_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'

if 'PyPy' in sys.version and _implementation_type == 'cpp':
  warnings.warn('PyPy does not work yet with cpp protocol buffers. '
                'Falling back to the python implementation.')
  _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.
_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)


# Detect if serialization should be deterministic by default
try:
  # The presence of this module in a build allows the proto implementation to
  # be upgraded merely via build deps.
  #
  # NOTE: Merely importing this automatically enables deterministic proto
  # serialization for C++ code, but we still need to export it as a boolean so
  # that we can do the same for `_implementation_type == 'python'`.
  #
  # NOTE2: It is possible for C++ code to enable deterministic serialization by
  # default _without_ affecting Python code, if the C++ implementation is not in
  # use by this module.  That is intended behavior, so we don't actually expose
  # this boolean outside of this module.
  #
  # pylint: disable=g-import-not-at-top,unused-import
  from google.protobuf import enable_deterministic_proto_serialization
  _python_deterministic_proto_serialization = True
except ImportError:
  _python_deterministic_proto_serialization = False


# 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


# For internal use only
def IsPythonDefaultSerializationDeterministic():
  return _python_deterministic_proto_serialization

# DO NOT USE: For migration and testing only. Will be removed when Proto3
# defaults to preserve unknowns.
if _implementation_type == 'cpp':
  try:
    # pylint: disable=g-import-not-at-top
    from google.protobuf.pyext import _message

    def GetPythonProto3PreserveUnknownsDefault():
      return _message.GetPythonProto3PreserveUnknownsDefault()

    def SetPythonProto3PreserveUnknownsDefault(preserve):
      _message.SetPythonProto3PreserveUnknownsDefault(preserve)
  except ImportError:
    # Unrecognized cpp implementation. Skipping the unknown fields APIs.
    pass
else:
  _python_proto3_preserve_unknowns_default = True

  def GetPythonProto3PreserveUnknownsDefault():
    return _python_proto3_preserve_unknowns_default

  def SetPythonProto3PreserveUnknownsDefault(preserve):
    global _python_proto3_preserve_unknowns_default
    _python_proto3_preserve_unknowns_default = preserve