blocks|key|1192775|text|它是从标准输入中读取的，它应该由键盘以流数据的形式提供。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1192776|它不需要提供文件，但是可以使用重定向作为标准输入。|offset|length|1192777|在Python中，readlines()方法读取整个流，然后在换行符处将其拆分，并创建每一行的列表。|style|CODE|1192778|lines+=+sys.stdin.readlines()|code-block|syntax|javascript|1192779|上面创建了一个名为行的列表，其中每个元素都是一行(由行字符的末尾确定)。|1192780|您可以在Python教程的输入输出部分上阅读更多有关这方面的内容。|1192781|如果要提示用户输入，请使用input()方法(在Python2中，使用raw_input())：|1192782|user_input+=+input('Please+enter+something:+')
print('You+entered:+{}'.format(user_input))|1192783|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Redirection_(computing)|1|https://docs.python.org/2/tutorial/inputoutput.html^0|0|F|3|0|0|9|B|0|0|0|D|6|1|0|D|7|Z|B|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@$D|18|E|19|1|1A]]|A|$]]|$1|F|3|G|5|6|7|1B|8|@$D|1C|E|1D|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|1E|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1F|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1G|8|@]|9|@$D|1H|E|1I|1|1J]]|A|$]]|$1|S|3|T|5|6|7|1K|8|@$D|1L|E|1M|H|I]|$D|1N|E|1O|H|I]]|9|@]|A|$]]|$1|U|3|V|5|L|7|1P|8|@]|9|@]|A|$M|N]]|$1|W|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]]|X|$Y|$5|Z|10|11|A|$12|13]]|14|$5|Z|10|11|A|$12|15]]]]

It is reading from the standard input - and it should be provided by the keyboard in the form of stream data.

It is not required to provide a file, however you can use <a href="http://en.wikipedia.org/wiki/Redirection_(computing)" rel="noreferrer">redirection</a> to use a file as standard input.

In Python, the <code>readlines()</code> method reads the entire stream, and then splits it up at the newline character and creates a list of each line.

<pre><code>lines = sys.stdin.readlines()
</code></pre>

The above creates a list called lines, where each element will be a line (as determined by the end of line character).

You can read more about this at the <a href="https://docs.python.org/2/tutorial/inputoutput.html" rel="noreferrer">input and output section</a> of the Python tutorial.

If you want to prompt the user for input, use the <code>input()</code> method (in Python 2, use <code>raw_input()</code>):

<pre><code>user_input = input('Please enter something: ')
print('You entered: {}'.format(user_input))
</code></pre>

blocks|key|1192801|text|for+something+in+sys.stdin:
++++some+stuff+here|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1192802|上面的代码不像您预期的那样工作，因为sys.stdin是一个文件句柄--它是stdin的文件句柄。它不会到达some+stuff+here线|unstyled|offset|length|style|CODE|1192803|lines+=+sys.stdin.readlines()|1192804|当上面的脚本在一个交互式shell中运行时，它将阻止执行，直到用户按下Ctrl，这表示输入的结束。|1192805|entityMap^0|0|I|9|12|5|1I|F|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@$G|S|H|T|I|J]|$G|U|H|V|I|J]|$G|W|H|X|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|M|3|N|5|F|7|Z|8|@]|9|@]|A|$]]|$1|O|3|-4|5|F|7|10|8|@]|9|@]|A|$]]]|P|$]]

<pre><code>for something in sys.stdin:
 some stuff here
</code></pre>

The code above does not work as you expect because <code>sys.stdin</code> is a file handle - it is a file handle to the <code>stdin</code>. It will not reach the <code>some stuff here</code> line

<pre><code>lines = sys.stdin.readlines()
</code></pre>

When the script above is run in an interactive shell, it will block the execution until a user presses Ctrl-D, which indicates the end of the input.

blocks|key|145898|text|因此，您已经使用了Python的“预内置函数”，大概如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|145899|file_object+=+open('filename')
for+something+in+file_object:
++++some+stuff+here|code-block|syntax|javascript|145900|它通过调用文件对象上的迭代器来读取文件，而文件对象恰好从文件返回下一行。|145901|相反，您可以使用：|145902|file_object+=+open('filename')
lines+=+file_object.readlines()|145903|它将当前文件位置中的行读入列表。|145904|现在，sys.stdin只是另一个文件对象，它恰好是在程序启动之前由Python打开的。您如何处理该文件对象取决于您自己，但它与任何其他文件对象并没有什么不同，只是您不需要一个open。|offset|length|style|CODE|145905|for+something+in+sys.stdin:
++++some+stuff+here|145906|将遍历标准输入，直到文件结束为止。这一点也是如此：|145907|lines+=+sys.stdin.readlines()|145908|您的第一个问题实际上是关于使用文件对象的不同方式。|145909|第二，它是从哪里读来的？它正在读取文件描述符0(零)。在Windows上，它是文件句柄0(零)。默认情况下，文件描述符/句柄0连接到控制台或tty，因此它实际上是从键盘读取的。但是，它可以被重定向，通常由shell+(如bash或cmd.exe)使用如下语法：|145910|myprog.py+<+input_file.txt+|145911|它将文件描述符更改为零，以读取文件而不是键盘。在UNIX或Linux上，这使用底层调用dup2()。阅读您的shell文档，了解更多关于重定向的信息(或者，如果您勇敢，可以阅读man+dup2+)。|145912|entityMap^0|0|0|0|0|0|0|3|9|2G|4|0|0|0|0|0|0|0|17|6|2G|8|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1C|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1D|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|1F|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1G|8|@$Q|1H|R|1I|S|T]|$Q|1J|R|1K|S|T]]|9|@]|A|$]]|$1|U|3|V|5|D|7|1L|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1M|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1N|8|@]|9|@]|A|$E|F]]|$1|10|3|11|5|6|7|1O|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1P|8|@]|9|@]|A|$]]|$1|14|3|15|5|D|7|1Q|8|@]|9|@]|A|$E|F]]|$1|16|3|17|5|6|7|1R|8|@$Q|1S|R|1T|S|T]|$Q|1U|R|1V|S|T]]|9|@]|A|$]]|$1|18|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]]|19|$]]

So you have used Python's "pre built in functions", presumably like this:

<pre><code>file_object = open('filename')
for something in file_object:
 some stuff here
</code></pre>

This reads the file by invoking an iterator on the file object which happens to return the next line from the file. 

You could instead use:

<pre><code>file_object = open('filename')
lines = file_object.readlines()
</code></pre>

which reads the lines from the current file position into a list.

Now, <code>sys.stdin</code> is just another file object, which happens to be opened by Python before your program starts. What you do with that file object is up to you, but it is not really any different to any other file object, its just that you don't need an <code>open</code>.

<pre><code>for something in sys.stdin:
 some stuff here
</code></pre>

will iterate through standard input until end-of-file is reached. And so will this:

<pre><code>lines = sys.stdin.readlines()
</code></pre>

Your first question is really about different ways of using a file object. 

Second, where is it reading from? It is reading from file descriptor 0 (zero). On Windows it is file handle 0 (zero). File descriptor/handle 0 is connected to the console or tty by default, so in effect it is reading from the keyboard. However it can be redirected, often by a shell (like bash or cmd.exe) using syntax like this:

<pre><code>myprog.py &lt; input_file.txt 
</code></pre>

That alters file descriptor zero to read a file instead of the keyboard. On UNIX or Linux this uses the underlying call <code>dup2()</code>. Read your shell documentation for more information about redirection (or maybe <code>man dup2</code> if you are brave).

blocks|key|2490312|text|要了解sys.stdin的工作原理，请执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2490313|创建一个简单的python脚本，让我们将其命名为"readStdin.py"：|2490314|import+sys
lines+=+sys.stdin.readlines()
print+(lines)|code-block|syntax|javascript|2490315|现在打开控制台，任何类型的：|2490316|echo+"line1+line2+line3"+%7C+python+readStdin.py|2490317|脚本输出：|2490318|['"line1+line2+line3"+\n']|2490319|因此，脚本将输入读入列表(名为“line”)，包括由“echo”生成的新行字符。那是。|2490320|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

To get a grasp how sys.stdin works do following:

create a simple python script, let's name it "readStdin.py":

<pre><code>import sys
lines = sys.stdin.readlines()
print (lines)
</code></pre>

Now open console any type in:

<pre><code>echo "line1 line2 line3" | python readStdin.py
</code></pre>

The script outputs:

<pre><code>['"line1 line2 line3" \n']
</code></pre>

So, the script has read the input into list (named 'lines'), including the new line character produced by 'echo'. That is.

blocks|key|1192895|text|它将逐行读取源文件。它被广泛应用于在线裁判系统中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1192896|例如:假设文件中只使用一个数字2。|offset|length|style|CODE|1192897|import+sys

if+__name__+==+"__main__":
++++n+=+int(sys.stdin.readline().strip())|code-block|syntax|javascript|1192898|逐行读取文件意味着读取数字2+(在本例中只有一行)。使用该条删除不需要的空格或其他指定字符。这将导致n=(整数)+2。|1192899|如果我们有一个两行的文件，如下所示：|1192900|1
2|1192901|然后，sys.stdin.readline().strip()将其转换为一行(名为n的列表)，其中包含两个元素1，2。那么我们现在不能使用int转换器了，但是我们可以使用int(n[0])和int(n[1])。|1192902|entityMap^0|0|F|1|0|0|D|1|1L|1|0|0|0|3|S|15|1|1J|1|1L|1|1X|3|2D|9|2N|9|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@$D|12|E|13|F|G]|$D|14|E|15|F|G]]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|R|5|J|7|17|8|@]|9|@]|A|$K|L]]|$1|S|3|T|5|6|7|18|8|@$D|19|E|1A|F|G]|$D|1B|E|1C|F|G]|$D|1D|E|1E|F|G]|$D|1F|E|1G|F|G]|$D|1H|E|1I|F|G]|$D|1J|E|1K|F|G]|$D|1L|E|1M|F|G]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|V|$]]

It will read the source file line by line. It is widely used in Online Judge System.
For example: suppose we have only one number <code>2</code> will be used in the file.
<pre class="lang-py prettyprint-override"><code>import sys

if __name__ == &quot;__main__&quot;:
 n = int(sys.stdin.readline().strip())
</code></pre>
Read the file line by line means read the number <code>2</code> (only one line in this case). Using the strip to remove unneeded space or other specified characters. This will result in n = (integer) <code>2</code>.
If we have a file with two lines like:
<pre><code>1
2
</code></pre>
Then, <code>sys.stdin.readline().strip()</code> will transform it to one line (a list, named <code>n</code>) with two elements <code>1</code>, <code>2</code>. Then we cannot use <code>int</code> transformer now but we can use <code>int(n[0])</code> and <code>int(n[1])</code> instead.

I get how to open files, and then use Python's pre built in functions with them. But how does sys.stdin work? 

<pre><code>for something in sys.stdin:
 some stuff here

lines = sys.stdin.readlines()
</code></pre>

What's the difference between the above two different uses on sys.stdin? Where is it reading the information from? Is it via keyboard, or do we still have to provide a file?

What does sys.stdin read?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我了解了如何打开文件，然后将Python的预内置函数与它们一起使用。但是sys.stdin是如何工作的呢？for something in sys.stdin:    some stuff herelines = sys.stdin.readlines()以上两种不同用途在sys.stdin上的区别是什么？它在哪里读取...

问sys.stdin读什么？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问sys.stdin读什么？EN