code: def sanitize_label(text):
      
      if not text:
          return text
      text = re.sub('\\W+', '_', text)
      if text[0] in string.digits:
          text = "key_" + text
      elif text[0] == '_':
          text = "key" + text
      return text[:100]
docs: Remove characters not accepted in labels key
  
      This replaces any non-word characters (alphanumeric or underscore), with
      an underscore. It also ensures that the first character is a letter by
      prepending with 'key' if necessary, and trims the text to 100 characters.