code: def _AddFileDescriptor(self, file_desc):
      
  
      if not isinstance(file_desc, descriptor.FileDescriptor):
        raise TypeError('Expected instance of descriptor.FileDescriptor.')
      self._file_descriptors[file_desc.name] = file_desc
docs: Adds a FileDescriptor to the pool, non-recursively.
  
      If the FileDescriptor contains messages or enums, the caller must explicitly
      register them.
  
      Args:
        file_desc: A FileDescriptor.