docs: def is_user(value, min=None, max=None):
      """
      Check whether username or uid as argument exists.
      if this function recieved username, convert uid and exec validation.
      """
  
      if type(value) == str:
          try:
              entry = pwd.getpwnam(value)
              value = entry.pw_uid
          except KeyError:
              err_message = ('{0}: No such user.'.format(value))
              raise validate.VdtValueError(err_message)
  
          return value
  
      elif type(value) == int:
          try:
              pwd.getpwuid(value)
          except KeyError:
              err_message = ('{0}: No such user.'.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)