1# Protocol Buffers - Google's data interchange format
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30
31"""A database of Python protocol buffer generated symbols.
32
33SymbolDatabase makes it easy to create new instances of a registered type, given
34only the type's protocol buffer symbol name. Once all symbols are registered,
35they can be accessed using either the MessageFactory interface which
36SymbolDatabase exposes, or the DescriptorPool interface of the underlying
37pool.
38
39Example usage:
40
41  db = symbol_database.SymbolDatabase()
42
43  # Register symbols of interest, from one or multiple files.
44  db.RegisterFileDescriptor(my_proto_pb2.DESCRIPTOR)
45  db.RegisterMessage(my_proto_pb2.MyMessage)
46  db.RegisterEnumDescriptor(my_proto_pb2.MyEnum.DESCRIPTOR)
47
48  # The database can be used as a MessageFactory, to generate types based on
49  # their name:
50  types = db.GetMessages(['my_proto.proto'])
51  my_message_instance = types['MyMessage']()
52
53  # The database's underlying descriptor pool can be queried, so it's not
54  # necessary to know a type's filename to be able to generate it:
55  filename = db.pool.FindFileContainingSymbol('MyMessage')
56  my_message_instance = db.GetMessages([filename])['MyMessage']()
57
58  # This functionality is also provided directly via a convenience method:
59  my_message_instance = db.GetSymbol('MyMessage')()
60"""
61
62
63from google.protobuf import descriptor_pool
64
65
66class SymbolDatabase(object):
67  """A database of Python generated symbols.
68
69  SymbolDatabase also models message_factory.MessageFactory.
70
71  The symbol database can be used to keep a global registry of all protocol
72  buffer types used within a program.
73  """
74
75  def __init__(self):
76    """Constructor."""
77
78    self._symbols = {}
79    self._symbols_by_file = {}
80    self.pool = descriptor_pool.DescriptorPool()
81
82  def RegisterMessage(self, message):
83    """Registers the given message type in the local database.
84
85    Args:
86      message: a message.Message, to be registered.
87
88    Returns:
89      The provided message.
90    """
91
92    desc = message.DESCRIPTOR
93    self._symbols[desc.full_name] = message
94    if desc.file.name not in self._symbols_by_file:
95      self._symbols_by_file[desc.file.name] = {}
96    self._symbols_by_file[desc.file.name][desc.full_name] = message
97    self.pool.AddDescriptor(desc)
98    return message
99
100  def RegisterEnumDescriptor(self, enum_descriptor):
101    """Registers the given enum descriptor in the local database.
102
103    Args:
104      enum_descriptor: a descriptor.EnumDescriptor.
105
106    Returns:
107      The provided descriptor.
108    """
109    self.pool.AddEnumDescriptor(enum_descriptor)
110    return enum_descriptor
111
112  def RegisterFileDescriptor(self, file_descriptor):
113    """Registers the given file descriptor in the local database.
114
115    Args:
116      file_descriptor: a descriptor.FileDescriptor.
117
118    Returns:
119      The provided descriptor.
120    """
121    self.pool.AddFileDescriptor(file_descriptor)
122
123  def GetSymbol(self, symbol):
124    """Tries to find a symbol in the local database.
125
126    Currently, this method only returns message.Message instances, however, if
127    may be extended in future to support other symbol types.
128
129    Args:
130      symbol: A str, a protocol buffer symbol.
131
132    Returns:
133      A Python class corresponding to the symbol.
134
135    Raises:
136      KeyError: if the symbol could not be found.
137    """
138
139    return self._symbols[symbol]
140
141  def GetPrototype(self, descriptor):
142    """Builds a proto2 message class based on the passed in descriptor.
143
144    Passing a descriptor with a fully qualified name matching a previous
145    invocation will cause the same class to be returned.
146
147    Args:
148      descriptor: The descriptor to build from.
149
150    Returns:
151      A class describing the passed in descriptor.
152    """
153
154    return self.GetSymbol(descriptor.full_name)
155
156  def GetMessages(self, files):
157    """Gets all the messages from a specified file.
158
159    This will find and resolve dependencies, failing if they are not registered
160    in the symbol database.
161
162
163    Args:
164      files: The file names to extract messages from.
165
166    Returns:
167      A dictionary mapping proto names to the message classes. This will include
168      any dependent messages as well as any messages defined in the same file as
169      a specified message.
170
171    Raises:
172      KeyError: if a file could not be found.
173    """
174
175    result = {}
176    for f in files:
177      result.update(self._symbols_by_file[f])
178    return result
179
180_DEFAULT = SymbolDatabase()
181
182
183def Default():
184  """Returns the default SymbolDatabase."""
185  return _DEFAULT
186