如何遍历文件的第n行? [英] How to iterate over every n-th line from a file?

问题描述

首先，我是Python的新手，确实可以找到答案，但是没有运气.到目前为止，我发现的内容只返回一行，就像下面的代码一样.我尝试了其他解决方案，例如 itertools.islice ，但始终只能返回一行.

First, I am new to Python and did search for answers, but no luck. So far what I found only returns a one line like my code below. I tried other solutions like itertools.islice but always only get a one line back.

我有一个名为 data.txt 的文件，其中包含数据行:

I have a file called data.txt containing lines of data:

This is line one
This is line two 
This is line three 
This is line four 
This is line five 
This is line six 
This is line seven 
...

我有以下代码:

with open('data.txt', 'r') as f:
    for x, line in enumerate(f):
        if x == 3:
            print(line)

在这种情况下，它仅打印

In this case it only prints

这是第四行".

我确实理解为什么，但是如何从这里拿走它并打印第4、7、10、13，...行?

I do understand why but how do I take it from here and have it print the lines 4, 7, 10, 13, ...?

推荐答案

islice(可迭代，开始，停止[，步骤])->islice对象
返回一个迭代器，该迭代器的next()方法从可迭代的.[...]

islice(iterable, start, stop[, step]) --> islice object
Return an iterator whose next() method returns selected values from an iterable. [...]

演示:

data.txt :

line1
line2
line3
line4
line5
line6
line7
line8
line9
line10
line11
line12
line13

代码:

from itertools import islice

with open('data.txt') as f:
    for line in islice(f, 3, None, 3):
        print line,  # Python3: print(line, end='')

产生:

line4
line7
line10
line13

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