我正在使用for循环来读取文件，但我只想读取python中的特定行 [英] I'm using a for loop to read a file, but I only want to read specific lines in python

问题描述

我正在使用for循环来读取文件，但我只想读取特定行，比如第26行和第30行。是否有任何内置功能来实现这一目标？

I'm using a for loop to read a file, but I only want to read specific lines, say line #26 and #30. Is there any built-in feature to achieve this?

推荐答案

就像谢尔盖所说，你必须阅读所有的内容，至少在你读完之前你想要什么。

然而，你可以使用Linq让它变得非常简单：

Like Sergey said, you'll have to read all of the lines, at least until you've read what you wanted.
However, you can use Linq to make it pretty easy:

List<int> myLineNumbers = new List<int>{26, 30};    // 0-based line numbers!!!
IEnumerable<string> justMyLines = File.ReadLines("pathFileName").Where((text, lineNum) => myLineNumbers.Contains(lineNum));

如果 myLineNumbers ，然后，而不是 List< int> ，使用 HashSet< int> 或 BitArray 会更有效。

If you have a large number of values in myLineNumbers, then, instead of List<int>, using a HashSet<int> or BitArray would be more efficient.

不幸的是，你仍然需要读取所有行，至少到你提取的位置你需要的信息。



原因很简单：所有行的长度可以不同，它们由行尾定义文件内容中的字符。在读取行至少一次之前，您不知道行结束在文件中的位置。



另请参阅： http：//en.wikipedia .org / wiki /行尾 [ ^ ]。

-SA

Unfortunately, you still have to read all lines, at least to the point where you extract the piece of information you need.

The reason for that is very simple: the lengths of all lines can be different, they are defined by the end-of-line characters in the content of your file. Before you read the lines at least once, you don't know where the line ends are located in your file.

See also: http://en.wikipedia.org/wiki/End-of-line[^].

—SA

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