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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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:
      descriptor_name = descriptor.name
      if str is bytes:  # PY2
        descriptor_name = descriptor.name.encode('ascii', 'ignore')
      result_class = reflection.GeneratedProtocolMessageType(
          descriptor_name,
          (message.Message,),
          {'DESCRIPTOR': descriptor, '__module__': None})
          # If module not set, it wrongly points to the reflection.py module.
      self._classes[descriptor.full_name] = result_class
      for field in descriptor.fields:
        if field.message_type:
          self.GetPrototype(field.message_type)
      for extension in result_class.DESCRIPTOR.extensions:
        if extension.containing_type.full_name not in self._classes:
          self.GetPrototype(extension.containing_type)
        extended_class = self._classes[extension.containing_type.full_name]
        extended_class.RegisterExtension(extension)
    return self._classes[descriptor.full_name]