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reflection.py
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# Protocol Buffers - Google's data interchange format # Copyright 2008 Google Inc. All rights reserved. # https://developers.google.com/protocol-buffers/ # # Redistribution and use in source and binary forms, with or without # modification, are permitted provided that the following conditions are # met: # # * Redistributions of source code must retain the above copyright # notice, this list of conditions and the following disclaimer. # * Redistributions in binary form must reproduce the above # copyright notice, this list of conditions and the following disclaimer # in the documentation and/or other materials provided with the # distribution. # * Neither the name of Google Inc. nor the names of its # contributors may be used to endorse or promote products derived from # this software without specific prior written permission. # # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. # This code is meant to work on Python 2.4 and above only. """Contains a metaclass and helper functions used to create protocol message classes from Descriptor objects at runtime. Recall that a metaclass is the "type" of a class. (A class is to a metaclass what an instance is to a class.) In this case, we use the GeneratedProtocolMessageType metaclass to inject all the useful functionality into the classes output by the protocol compiler at compile-time. The upshot of all this is that the real implementation details for ALL pure-Python protocol buffers are *here in this file*. """ __author__ = 'robinson@google.com (Will Robinson)' from google.protobuf.internal import api_implementation from google.protobuf import message if api_implementation.Type() == 'cpp': from google.protobuf.pyext import cpp_message as message_impl else: from google.protobuf.internal import python_message as message_impl # The type of all Message classes. # Part of the public interface, but normally only used by message factories. GeneratedProtocolMessageType = message_impl.GeneratedProtocolMessageType MESSAGE_CLASS_CACHE = {} def ParseMessage(descriptor, byte_str): """Generate a new Message instance from this Descriptor and a byte string. Args: descriptor: Protobuf Descriptor object byte_str: Serialized protocol buffer byte string Returns: Newly created protobuf Message object. """ result_class = MakeClass(descriptor) new_msg = result_class() new_msg.ParseFromString(byte_str) return new_msg def MakeClass(descriptor): """Construct a class object for a protobuf described by descriptor. Composite descriptors are handled by defining the new class as a member of the parent class, recursing as deep as necessary. This is the dynamic equivalent to: class Parent(message.Message): __metaclass__ = GeneratedProtocolMessageType DESCRIPTOR = descriptor class Child(message.Message): __metaclass__ = GeneratedProtocolMessageType DESCRIPTOR = descriptor.nested_types[0] Sample usage: file_descriptor = descriptor_pb2.FileDescriptorProto() file_descriptor.ParseFromString(proto2_string) msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0]) msg_class = reflection.MakeClass(msg_descriptor) msg = msg_class() Args: descriptor: A descriptor.Descriptor object describing the protobuf. Returns: The Message class object described by the descriptor. """ if descriptor in MESSAGE_CLASS_CACHE: return MESSAGE_CLASS_CACHE[descriptor] attributes = {} for name, nested_type in descriptor.nested_types_by_name.items(): attributes[name] = MakeClass(nested_type) attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor result = GeneratedProtocolMessageType( str(descriptor.name), (message.Message,), attributes) MESSAGE_CLASS_CACHE[descriptor] = result return result