def tokens(self, format_string):
        """
        Get the tokenized format_string.
        Tokenizing is resource intensive so we only do it once and cache it
        """
        if format_string not in self.format_string_cache:
            tokens = list(re.finditer(self.reg_ex, format_string))
            self.format_string_cache[format_string] = tokens
        return self.format_string_cache[format_string]

        Get the tokenized format_string.
        Tokenizing is resource intensive so we only do it once and cache it
        
py3status/formatter.py