def update_placeholder_formats(self, format_string, placeholder_formats):
        """
        Update a format string adding formats if they are not already present.
        """
        # Tokenize the format string and process them
        output = []
        for token in self.tokens(format_string):
            if (
                token.group("placeholder")
                and (not token.group("format"))
                and token.group("key") in placeholder_formats
            ):
                output.append(f"{{{token.group('key')}{placeholder_formats[token.group('key')]}}}")
                continue
            value = token.group(0)
            output.append(value)
        return "".join(output)

        Update a format string adding formats if they are not already present.
        
py3status/formatter.py