code: def convert(self, vroot, entry_variables):
          
  
          for converter in self.converters:
              vroot = converter.convert(vroot, entry_variables)
          return vroot
docs: Convert a given graph.
  
          Convert a given graph using the `converters` in the order of the registeration, i.e., sequentially.
  
          Args:
              vroot (:obj:`Variable`): NNabla Variable
              entry_variables (:obj:`Variable`): Entry variable from which the conversion starts.