human
Solve the following python programming problem given the following code:
def _alias_columns(self, sql) : 
    'Return tuple of SELECT and FROM clauses, aliasing duplicate column names.' 
    qn = self.connection.ops.quote_name 
    outer = list () 
    inner = list () 
    names_seen = list () 
    (paren_depth, paren_buf) = (0, ['']) 
    (parens, i) = ({ 
        
}, 0) 
    for ch in sql : 
        if (ch == '(') : 
            i += 1 
            paren_depth += 1 
            paren_buf.append ('') 
else : 
            if (ch == ')') : 
                paren_depth -= 1 
                key = '_placeholder_{0}'.format (i) 
                buf = paren_buf.pop () 
                buf = re.sub ('%([^\\(])', '$$$\\1', buf) 
                parens [key] = (buf % parens) 
                parens [key] = re.sub ('\\$\\$\\$([^\\(])', '%\\1', parens [key]) 
                paren_buf [paren_depth] += (('(%(' + key) + ')s)') 
else : 
                paren_buf [paren_depth] += ch 
def _replace_sub(col) : 
        'Replace all placeholders with expanded values' 
        while _re_col_placeholder.search (col) : 
            col = col.format (** parens) 
return col 
temp_sql = ''.join (paren_buf) 
    placeholder_data = { 
        'i' : i, 
} 
    def _alias_placeholders(val) : 
        i = placeholder_data ['i'] 
        i += 1 
        placeholder_data ['i'] = i 
        key = '_placeholder_{0}'.format (i) 
        parens [key] = '%s' 
        return (('%(' + key) + ')s') 
temp_sql = re.sub ('%s', _alias_placeholders, temp_sql) 
    (select_list, from_clause) = _break (temp_sql, (' FROM ' + self.connection.ops.left_sql_quote)) 
    for col in [x.strip () for x in select_list.split (',')] : 
        match = self._re_pat_col.search (col) 
        if match : 
            col_name = match.group (1) 
            col_key = col_name.lower () 
            if (col_key in names_seen) : 
                alias = qn ('{0}___{1}'.format (col_name, names_seen.count (col_key))) 
                outer.append (alias) 
                inner.append ('{0} as {1}'.format (_replace_sub (col), alias)) 
else : 
    ...

    
    

    Fix the buggy line: names_seen.append (col_name)
assistant
#Here is Python program to fix the buggy line: names_seen.

names_seen.append (col_key)