code: def set_completions(self, completions, go_to_first=True, go_to_last=False):
          
          assert not (go_to_first and go_to_last)
  
          # Generate list of all completions.
          if completions is None:
              if self.completer:
                  completions = list(self.completer.get_completions(
                      self.document,
                      CompleteEvent(completion_requested=True)
                  ))
              else:
                  completions = []
  
          # Set `complete_state`.
          if completions:
              self.complete_state = CompletionState(
                  original_document=self.document,
                  current_completions=completions)
              if go_to_first:
                  self.go_to_completion(0)
              elif go_to_last:
                  self.go_to_completion(len(completions) - 1)
              else:
                  self.go_to_completion(None)
  
          else:
              self.complete_state = None
docs: Start completions. (Generate list of completions and initialize.)