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//usr/lib/python2.7/site-packages/google/protobuf/message_factory.py

# Protocol Buffers - Google's data interchange format
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# http://code.google.com/p/protobuf/
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"""Provides a factory class for generating dynamic messages."""

__author__ = 'matthewtoia@google.com (Matt Toia)'

from google.protobuf import descriptor_database
from google.protobuf import descriptor_pool
from google.protobuf import message
from google.protobuf import reflection

class MessageFactory(object):
  """Factory for creating Proto2 messages from descriptors in a pool."""

def __init__(self):
    """Initializes a new factory."""
    self._classes = {}

def GetPrototype(self, descriptor):
    """Builds a proto2 message class based on the passed in descriptor.

Passing a descriptor with a fully qualified name matching a previous
    invocation will cause the same class to be returned.

Args:
      descriptor: The descriptor to build from.

Returns:
      A class describing the passed in descriptor.
    """

if descriptor.full_name not in self._classes:
      result_class = reflection.GeneratedProtocolMessageType(
          descriptor.name.encode('ascii', 'ignore'),
          (message.Message,),
          {'DESCRIPTOR': descriptor})
      self._classes[descriptor.full_name] = result_class
      for field in descriptor.fields:
        if field.message_type:
          self.GetPrototype(field.message_type)
    return self._classes[descriptor.full_name]

_DB = descriptor_database.DescriptorDatabase()
_POOL = descriptor_pool.DescriptorPool(_DB)
_FACTORY = MessageFactory()

def GetMessages(file_protos):
  """Builds a dictionary of all the messages available in a set of files.

Args:
    file_protos: A sequence of file protos to build messages out of.

Returns:
    A dictionary containing all the message types in the files mapping the
    fully qualified name to a Message subclass for the descriptor.
  """

result = {}
  for file_proto in file_protos:
    _DB.Add(file_proto)
  for file_proto in file_protos:
    for desc in _GetAllDescriptors(file_proto.message_type, file_proto.package):
      result[desc.full_name] = _FACTORY.GetPrototype(desc)
  return result

def _GetAllDescriptors(desc_protos, package):
  """Gets all levels of nested message types as a flattened list of descriptors.

Args:
    desc_protos: The descriptor protos to process.
    package: The package where the protos are defined.

Yields:
    Each message descriptor for each nested type.
  """

for desc_proto in desc_protos:
    name = '.'.join((package, desc_proto.name))
    yield _POOL.FindMessageTypeByName(name)
    for nested_desc in _GetAllDescriptors(desc_proto.nested_type, name):
      yield nested_desc