This converts '(' and ')' brackets the EDUs of the RST into PTB-style
    tokens (e.g., -LRB-) to escape them for nltk.

def convert_parens_in_rst_tree_str(rst_tree_str):
    '''
    This converts '(' and ')' brackets the EDUs of the RST into PTB-style
    tokens (e.g., -LRB-) to escape them for nltk.
    '''
    def replace_brackets(matchobj):
        edu = matchobj.group(0)
        for (br, br_repl) in DIS_ESCAPES:
            edu = re.sub("\{}".format(br), br_repl, edu)
        return edu

    return re.sub('_!(.*?)_!', replace_brackets, rst_tree_str)