def get_placeholders(self, format_string):
        """
        Parses the format_string and returns a set of placeholders.
        """
        placeholders = set()
        # Tokenize the format string and process them
        for token in self.tokens(format_string):
            if token.group("placeholder"):
                placeholders.add(token.group("key"))
            elif token.group("command"):
                # get any placeholders used in commands
                commands = dict(parse_qsl(token.group("command")))
                # placeholders only used in `if`
                if_ = commands.get("if")
                if if_:
                    placeholders.add(Condition(if_).variable)
        return placeholders

        Parses the format_string and returns a set of placeholders.
        
py3status/formatter.py