1# Protocol Buffers - Google's data interchange format
2# Copyright 2008 Google Inc.  All rights reserved.
3# http://code.google.com/p/protobuf/
4#
5# Redistribution and use in source and binary forms, with or without
6# modification, are permitted provided that the following conditions are
7# met:
8#
9#     * Redistributions of source code must retain the above copyright
10# notice, this list of conditions and the following disclaimer.
11#     * Redistributions in binary form must reproduce the above
12# copyright notice, this list of conditions and the following disclaimer
13# in the documentation and/or other materials provided with the
14# distribution.
15#     * Neither the name of Google Inc. nor the names of its
16# contributors may be used to endorse or promote products derived from
17# this software without specific prior written permission.
18#
19# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31"""
32This module is the central entity that determines which implementation of the
33API is used.
34"""
35
36__author__ = 'petar@google.com (Petar Petrov)'
37
38import os
39# This environment variable can be used to switch to a certain implementation
40# of the Python API. Right now only 'python' and 'cpp' are valid values. Any
41# other value will be ignored.
42_implementation_type = os.getenv('PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION',
43                                 'python')
44
45
46if _implementation_type != 'python':
47  # For now, by default use the pure-Python implementation.
48  # The code below checks if the C extension is available and
49  # uses it if it is available.
50  _implementation_type = 'cpp'
51  ## Determine automatically which implementation to use.
52  #try:
53  #  from google.protobuf.internal import cpp_message
54  #  _implementation_type = 'cpp'
55  #except ImportError, e:
56  #  _implementation_type = 'python'
57
58
59# This environment variable can be used to switch between the two
60# 'cpp' implementations. Right now only 1 and 2 are valid values. Any
61# other value will be ignored.
62_implementation_version_str = os.getenv(
63    'PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION',
64    '1')
65
66
67if _implementation_version_str not in ('1', '2'):
68  raise ValueError(
69      "unsupported PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION_VERSION: '" +
70      _implementation_version_str + "' (supported versions: 1, 2)"
71      )
72
73
74_implementation_version = int(_implementation_version_str)
75
76
77
78# Usage of this function is discouraged. Clients shouldn't care which
79# implementation of the API is in use. Note that there is no guarantee
80# that differences between APIs will be maintained.
81# Please don't use this function if possible.
82def Type():
83  return _implementation_type
84
85# See comment on 'Type' above.
86def Version():
87  return _implementation_version
88