code: def format_formula(formula):
      
  
      formatted_formula = ""
      number_format = ""
      for i, s in enumerate(formula):
          if s.isdigit():
              if not number_format:
                  number_format = "_{"
              number_format += s
              if i == len(formula) - 1:
                  number_format += "}"
                  formatted_formula += number_format
          else:
              if number_format:
                  number_format += "}"
                  formatted_formula += number_format
                  number_format = ""
              formatted_formula += s
  
      return r"$%s$" % (formatted_formula)
docs: Converts str of chemical formula into
      latex format for labelling purposes
  
      Args:
          formula (str): Chemical formula