python for循环的复合语句

有以下几种方式：

    # nested if
    for l in lines:
        if l.startswith('example'):
            body
    # continue,to put an accent on exceptional case
    for l in lines:
        if not l.startswith('example'):
            continue
        body
    # hacky way of generator expression
    # (better than comprehension as does not store a list)
    for l in (l for l in lines if l.startswith('example')):
        body()
    # 或者
    for l in [l for l in lines if l.startswith('example')]:
        statements
    # and its named version
    def gen(lines):
        return (l for l in lines if l.startswith('example'))
    for line in gen(lines):
        body
    # functional style
    for line in filter(lambda l: l.startswith('example'),lines):
        body()

值得注意的是下面这种形式python语法中不存在，会报错：

    for line in lines if line.startswith('example'):
        statements