python string operate, replace string in Regular Expression.

replace_matched_part.py

def replace_matched_part(pattern, lstring, repl_str, group_name):
    """
    :param pattern:  类似 '.*?_(?P<char>\w)_\d\.\w+$'
    :param lstring:  需要替换的字符串
    :param repl_str: 匹配部分替换成的字符串
    :param group_name:  匹配中的组名 char
    :return:
    """
    def _rep_func(m):
        return ''.join([m.string[:m.start(group_name)], repl_str, m.string[m.end(group_name):]])
    return re.sub(pattern, _rep_func, lstring)