code: def validate_excel_sheet_name(sheet_name):
      
  
      validate_null_string(sheet_name)
  
      if len(sheet_name) > __MAX_SHEET_NAME_LEN:
          raise InvalidLengthError(
              "sheet name is too long: expected<={:d}, actual={:d}".format(
                  __MAX_SHEET_NAME_LEN, len(sheet_name)
              )
          )
  
      unicode_sheet_name = _preprocess(sheet_name)
      match = __RE_INVALID_EXCEL_SHEET_NAME.search(unicode_sheet_name)
      if match is not None:
          raise InvalidCharError(
              "invalid char found in the sheet name: '{:s}'".format(re.escape(match.group()))
          )
docs: :param str sheet_name: Excel sheet name to validate.
      :raises pathvalidate.NullNameError: If the ``sheet_name`` is empty.
      :raises pathvalidate.InvalidCharError:
          If the ``sheet_name`` includes invalid char(s):
          |invalid_excel_sheet_chars|.
      :raises pathvalidate.InvalidLengthError:
          If the ``sheet_name`` is longer than 31 characters.