Question

我有：

with open(self.corpus_file) as infile:
    for line in infile:

如何确定line是否是infile的最后一行？

如果重要的话，这就是Python 3.6。

Answer 1

这是一种简单的方法：

from itertools import tee

with open(self.corpus_file) as infile:
    infile, check = tee(infile)
    try:
        next(check)
    except StopIteration:
        # file is empty
    for line in infile:
        try:
            next(check)
        except StopIteration:
            # line is the last line

如果您不必停留在循环中，则是另一种甚至更简单的方法：

with open(self.corpus_file) as infile:
    for line in infile:
        pass

# line is now the last line

Answer 2

open返回的文件对象是Python中的迭代器，因此您可以在进行StopIteration来消耗next循环中的行的同时注意while：

with open(self.corpus_file) as f: 
    line = None 
    while True: 
        try: 
            line = next(f) 
        except StopIteration: 
            break

现在line应该包含最后一行。

Answer 3

通常，您不想尝试在循环内部弄清楚这一点，但是，当循环退出时，您会知道已经到了尽头。如果您想在结束时做一些特别的事情（有时可能break跳出循环），则可以在else上添加for子句：

with open(filename) as file:
    for line in file:
        if not do_stuff(line):
            break
    else: # got to the end without breaking
        do_something_special_with_last_line(line)

Answer 4

利用文件是迭代器的事实，可以使用以下通用配方。它与每行一起返回状态标志。基础迭代器的最后一个元素的标志为True：

def is_last(iterator):
    prev = next(iterator)  # immediate StopIteration possible
    for item in iterator:
        yield False, prev
        prev = item
    yield True, prev

您会喜欢使用它

with open(...) as infile:
    for last, line in is_last(infile):
        ...

Answer 5

您可以像这样使用collections.deque：

from collections import deque


def read_file(filename):
    with open(filename) as infile:
        dq = deque([next(infile)], 1)
        for line in infile:
            yield dq[0]
            dq.append(line)

    # Last line of file.
    yield 'LAST LINE: ' + dq[0]


corpus_file = 'corpus_file.txt'

for line in read_file(corpus_file):
    print(line, end='')

使用open（），如何判断我是否在文件的最后一行？

5 个答案: