Package google :: Package protobuf :: Module reflection
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Source Code for Module google.protobuf.reflection

  1  # Protocol Buffers - Google's data interchange format 
  2  # Copyright 2008 Google Inc.  All rights reserved. 
  3  # https://developers.google.com/protocol-buffers/ 
  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 
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 29  # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 30   
 31  # This code is meant to work on Python 2.4 and above only. 
 32   
 33  """Contains a metaclass and helper functions used to create 
 34  protocol message classes from Descriptor objects at runtime. 
 35   
 36  Recall that a metaclass is the "type" of a class. 
 37  (A class is to a metaclass what an instance is to a class.) 
 38   
 39  In this case, we use the GeneratedProtocolMessageType metaclass 
 40  to inject all the useful functionality into the classes 
 41  output by the protocol compiler at compile-time. 
 42   
 43  The upshot of all this is that the real implementation 
 44  details for ALL pure-Python protocol buffers are *here in 
 45  this file*. 
 46  """ 
 47   
 48  __author__ = 'robinson@google.com (Will Robinson)' 
 49   
 50   
 51  from google.protobuf.internal import api_implementation 
 52  from google.protobuf import message 
 53   
 54   
 55  if api_implementation.Type() == 'cpp': 
 56    from google.protobuf.pyext import cpp_message as message_impl 
 57  else: 
 58    from google.protobuf.internal import python_message as message_impl 
 59   
 60  # The type of all Message classes. 
 61  # Part of the public interface, but normally only used by message factories. 
 62  GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType 
 63   
 64   
65 -def ParseMessage(descriptor, byte_str):
66 """Generate a new Message instance from this Descriptor and a byte string. 67 68 Args: 69 descriptor: Protobuf Descriptor object 70 byte_str: Serialized protocol buffer byte string 71 72 Returns: 73 Newly created protobuf Message object. 74 """ 75 result_class = MakeClass(descriptor) 76 new_msg = result_class() 77 new_msg.ParseFromString(byte_str) 78 return new_msg
79 80
81 -def MakeClass(descriptor):
82 """Construct a class object for a protobuf described by descriptor. 83 84 Composite descriptors are handled by defining the new class as a member of the 85 parent class, recursing as deep as necessary. 86 This is the dynamic equivalent to: 87 88 class Parent(message.Message): 89 __metaclass__ = GeneratedProtocolMessageType 90 DESCRIPTOR = descriptor 91 class Child(message.Message): 92 __metaclass__ = GeneratedProtocolMessageType 93 DESCRIPTOR = descriptor.nested_types[0] 94 95 Sample usage: 96 file_descriptor = descriptor_pb2.FileDescriptorProto() 97 file_descriptor.ParseFromString(proto2_string) 98 msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0]) 99 msg_class = reflection.MakeClass(msg_descriptor) 100 msg = msg_class() 101 102 Args: 103 descriptor: A descriptor.Descriptor object describing the protobuf. 104 Returns: 105 The Message class object described by the descriptor. 106 """ 107 attributes = {} 108 for name, nested_type in descriptor.nested_types_by_name.items(): 109 attributes[name] = MakeClass(nested_type) 110 111 attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor 112 113 return GeneratedProtocolMessageType(str(descriptor.name), (message.Message,), 114 attributes)