def get_placeholders(self, format_string):
placeholders = set()<EOL>for token in self.tokens(format_string):<EOL><INDENT>if token.group("<STR_LIT>"):<EOL><INDENT>placeholders.add(token.group("<STR_LIT:key>"))<EOL><DEDENT>elif token.group("<STR_LIT>"):<EOL><INDENT>commands = dict(parse_qsl(token.group("<STR_LIT>")))<EOL>if_ = commands.get("<STR_LIT>")<EOL>if if_:<EOL><INDENT>placeholders.add(Condition(if_).variable)<EOL><DEDENT><DEDENT><DEDENT>return placeholders<EOL>
Parses the format_string and returns a set of placeholders.