def comment_lines(lines):
    ret = []
    for line in lines:
        ws_prefix, rest, ignore = RE_LINE_SPLITTER_COMMENT.match(line).groups()
        ret.append(ws_prefix + '#' + rest)
    return ''.join(ret)

# matches two main groups: 1) leading whitespace and 2) all following text
Return the intersection of two sets as a new set.
dataset/ETHPy150Open neovim/python-client/scripts/logging_statement_modifier.py/comment_lines--crossover with--dataset/ETHPy150Open azoft-dev-team/imagrium/env/Lib/sets.py/BaseSet.intersection