Question

假设我想处理文件的每一行，但最后一行需要特殊处理：

with open('my_file.txt') as f:
    for line in f:
        if <line is the last line>:
            handle_last_line(line)
        else:
            handle_line(line)

问题是，如何实施？似乎没有用于在Python中检测文件结尾的功能。

是否有另一种解决方案，而不是将行读入列表（使用f.readlines（）或类似方法）？

Answer 1

处理上一个行：

with open('my_file.txt') as f:
    line = None
    previous = next(f, None)
    for line in f:
        handle_line(previous)
        previous = line

    if previous is not None:
        handle_last_line(previous)

当循环终止时，您知道最后一行刚刚被读取。

通用版本，让您分别处理N个最后几行，使用collections.deque() object：

from collections import deque
from itertools import islice

with open('my_file.txt') as f:
    prev = deque(islice(f, n), n)
    for line in f:
        handle_line(prev.popleft())
        prev.append(line)

    for remaining in prev:
        handle_last_line(remaining)

Answer 2

您可以使用itertools.tee迭代迭代的两个副本：

next_lines, lines = itertools.tee(file_object)
next(next_lines)
for next_line, line in zip(next_lines, lines):
    handle_line(line)
last_line = next(lines, None)
if last_line is not None:
    handle_last_line(last_line)

在Python中，如何测试一行是否是最后一行？

2 个答案: