code: def concat_sheets(xl_path: str, sheetnames=None, add_tab_names=False):
      
      xl_path, choice = _check_xl_path(xl_path)
  
      if sheetnames is None:
          sheetnames = get_sheet_list(xl_path)
  
      sheets = pd.read_excel(xl_path, sheetname=sheetnames)
  
      if add_tab_names:
          for tab in sheets:
              sheets[tab]['Tab'] = [tab] * len(sheets[tab])
  
      return pd.concat([sheets[tab] for tab in sheets])
docs: Return a pandas DataFrame with the concat'ed
      content of the `sheetnames` from the Excel file in
      `xl_path`.
  
      Parameters
      ----------
      xl_path: str
          Path to the Excel file
  
      sheetnames: list of str
          List of existing sheet names of `xl_path`.
          If None, will use all sheets from `xl_path`.
  
      add_tab_names: bool
          If True will add a 'Tab' column which says from which
          tab the row comes from.
  
      Returns
      -------
      df: pandas.DataFrame