为什么我必须键入ctrl -d两次？ [英] Why do I have to type ctrl-d twice?

问题描述

出于我自己的娱乐，我已经编写了一个python脚本，该脚本使我可以将python用于bash单线；提供python生成器表达式；然后脚本对其进行迭代。这是脚本：

For my own amusement, I've cooked up a python script that allows me to use python for bash one-liners; Supply a python generator expression; and the script iterates over it. Here's the script:

DEFAULT_MODULES = ['os', 're', 'sys']

_g = {}
for m in DEFAULT_MODULES:
    _g[m] = __import__(m)

import sys
sys.stdout.writelines(eval(sys.argv[1], _g))

这就是您可能会使用它的方式。

And here's how you might use it.

$ groups | python pype.py '(l.upper() for l in sys.stdin)'
DBORNSIDE
$ 

对于预期用途，它可以完美地工作！

For the intended use, it works perfectly!

但是，当我不使用管道来填充它而直接调用它时，例如： _{[强调是为了显示我键入的内容]}

But when I don't feed it with pipe and just invoke it directly, for instance: _{[emphasis added to show what I type]}

$ python pype.py '("%r\n" % (l,) for l in sys.stdin)'
fooEnter
barEnter
bazEnter
Ctrl DCtrl D'foo\n'
'bar\n'
'baz\n'
$ 

为了停止接受输入并产生任何输出，我有输入 Enter - Ctrl D - Ctrl D 或 Ctrl D - Ctrl D - Ctrl D 。这违反了我的期望，应该按输入内容处理每一行，并且随时输入 Ctrl D 会结束脚本。我的理解力在哪里？

In order to stop accepting input and produce any output, I have to type either Enter - Ctrl D - Ctrl D or Ctrl D - Ctrl D - Ctrl D. This violates my expectations, that each line should be processed as entered, and that typing Ctrl D at any time will end the script. Where is the gap in my understanding?

编辑：我更新了交互式示例，以表明我在他的回答中看不到wim所描述的引文，还有一些

I've updated the interactive example to show that I'm not seeing the quoting wim describes in his answer, and some more examples too.

$ python pype.py '("%r\n" % (l,) for l in sys.stdin)'
fooCtrl DCtrl DbarEnter
Ctrl DCtrl D'foobar\n'
$ python pype.py '("%r\n" % (l,) for l in sys.stdin)'
fooCtrl VCtrl D^DbarEnter
Ctrl DCtrl D'foo\x04bar\n'
$ 

推荐答案

Ctrl-D 不一定识别为EOF，而是识别为终止当前 read（）呼叫。

Ctrl-D is recognized not necessarily as EOF, but as "terminate current read() call".

如果您有空行（或仅按 Ctrl-D ），然后按 Ctrl -D ，您的 read（）立即终止，并返回0个读取字节。

If you have an empty line (or just pressed Ctrl-D) and press Ctrl-D, your read() terminates immediately and returns 0 read bytes. And this is a sign for EOF.

如果一行中有数据并按 Ctrl-D ，则您的 read（）终止于任何键入的内容，当然没有终止换行符（'\n'）。

If you have data in a line and press Ctrl-D, your read() terminates with whatever there has been typed, of course without a terminating newline ('\n').

因此，如果您有输入数据，请按两次 Ctrl-D 两次非空行，或者在空行中按一次，即使用 Enter 之前。

So if you have input data, you press Ctrl-D twice of a non-empty line or once on a empty one, i.e. with Enter before.

所有这些都适用于普通的操作系统界面，可通过 os.read（）。

This all holds for the normal OS interface, accessible from Python via os.read().

Python文件对象以及文件迭代器，会将第一个EOF视为当前 read（）打电话，因为他们认为已经没有了。下一个 read（）调用将再次尝试，并且需要另一个 Ctrl-D 才能真正返回0字节。原因是文件对象 read（）总是尝试返回所请求的字节数，并在操作系统 read（）<时尝试填满/ code>返回的值小于请求的值。

Python file objects, and also file iterators, treat the first EOF recognized as termination for the current read() call, as they suppose there is nothing any longer. A next read() call tries again and needs another Ctrl-D in order to really return 0 bytes. The reason is that a file object read() always tries to return as many bytes as requested and tries to fill up if a OS read() returns less than requested.

与 file.readline（）相反， iter（file）使用内部的 read（）函数进行读取，因此总是对额外的有特殊要求Ctrl-D 。

As opposite to file.readline(), iter(file) uses the internal read() functions to read and thus always has this special requirement of the extra Ctrl-D.

我总是使用 iter（file.readline，''）进行读取从文件中逐行输入。

I always use iter(file.readline, '') to read line-wise from a file.

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