Question

我试图让python读取.txt文件的最后三行。我也试图将每一行添加为列表中的元素。

例如：

**list.txt**
line1
line2
line3

**python_program.py**
(read list.txt, insert items into line_list)
line_list[line1,line2,line3]

但是我对这个过程感到有点困惑。

非常感谢任何帮助！

Answer 1

如果您正在处理一个非常大的文件怎么办？阅读内存中的所有行将是非常浪费的。另一种方法可能是：

from collections import deque 
d=deque([], maxlen=3)
with open("file.txt") as f:
    for l in f:
       d.append(l)

这在给定时间内仅在读取的最后三行中保留在内存中（deque丢弃每个附加处的过多的最旧元素）。

正如@ user2357112指出的那样，这也会起作用，并且更具合成性：

from collections import deque 
d=None
with open("file.txt") as f:
    d=deque(f, maxlen=3)

Answer 2

with open('list.txt') as f:
    lines = f.readlines()
line_list = lines[-3:]

Answer 3

试试这些：

#!/usr/local/cpython-3.3/bin/python

import pprint

def get_last_3_variant_1(file_):
    # This is simple, but it also reads the entire file into memory
    lines = file_.readlines()
    return lines[-3:]

def get_last_3_variant_2(file_):
    # This is more complex, but it only keeps three lines in memory at any given time
    three_lines = []
    for index, line in zip(range(3), file_):
        three_lines.append(line)

    for line in file_:
        three_lines.append(line)
        del three_lines[0]

    return three_lines

get_last_3 = get_last_3_variant_2

def main():
    # /etc/services is a long file
    # /etc/adjtime is exactly 3 lines long on my system
    # /etc/libao.conf is exactly 2 lines long on my system
    for filename in ['/etc/services', '/etc/adjtime', '/etc/libao.conf']:
        with open (filename, 'r') as file_:
            result = get_last_3(file_)
        pprint.pprint(result)

main()

Python如何读取.txt文件的最后三行，并将这些项放入列表中？

3 个答案: