code: def is_group(value):
      
  
      if type(value) == str:
          try:
              entry = grp.getgrnam(value)
              value = entry.gr_gid
          except KeyError:
              err_message = ('{0}: No such group.'.format(value))
              raise validate.VdtValueError(err_message)
  
          return value
  
      elif type(value) == int:
          try:
              grp.getgrgid(value)
          except KeyError:
              err_message = ('{0}: No such group.'.format(value))
              raise validate.VdtValueError(err_message)
  
          return value
  
      else:
          err_message = ('Please, use str or int to "user" parameter.')
          raise validate.VdtTypeError(err_message)
docs: Check whether groupname or gid as argument exists.
      if this function recieved groupname, convert gid and exec validation.