code: def users(self, proc):
          
          ret = {}
          if self.first_column in ['USER', 'UID']:
              for row in self.data:
                  if proc == row[self.command_name]:
                      if row[self.first_column] not in ret:
                          ret[row[self.first_column]] = []
                      ret[row[self.first_column]].append(row["PID"])
          return ret
docs: Searches for all users running a given command.
  
          Returns:
              dict: each username as a key to a list of PIDs (as strings) that
              are running the given process.
              ``{}`` if  neither ``USER`` nor ``UID`` is found or ``proc`` is not found.
  
          .. note::
             'proc' must match the entire command and arguments.