msvcrt.getch（）方法中的\xe0是什么？ [英] What is \xe0 in the msvcrt.getch() method?
问题描述
在msvcrt.getch（）方法中，当我输入ascii表中没有的任何值时，我总是得到 \xe0。我不知道这是什么意思
In the msvcrt.getch() method, when I enter any value that isn't in the ascii table, I get '\xe0' all the time. I don't know what this means
>>>import msvcrt
>>>up_arrow = msvcrt.getch()
>>> # this is where I have inputed the up arrow
>>>print up_arrow
'\xe0'
>>>down_arrow = msvcrt.getch()
>>>
>>>print down_arrow
'\xe0'
推荐答案
这在文档中进行了解释：
如果按下的键是特殊功能键，则将返回 \000或 \xe0 ';
If the pressed key was a special function key, this will return '\000' or '\xe0'; the next call will return the keycode.
如您所见，您可以从源，Python只是调用了MSVCRT函数 _getch ，有点像POSIX函数 getch ，但在一个按键方式上有所不同：
Under the covers, as you can see from the source, Python is just calling the MSVCRT function _getch, which is sort of like the POSIX function getch, but different in one key way:
读取功能键或箭头键时，每个功能必须被两次叫过第一次调用返回0或0xE0，第二次调用返回实际的密钥代码。
When reading a function key or an arrow key, each function must be called twice; the first call returns 0 or 0xE0, and the second call returns the actual key code.
其历史原因可追溯到DOS Windows NT 3.x中的兼容性（或者，对于Windows NT，Microsoft C ++中的DOS兼容性，是Turbo C）。
The historical reason for this goes back to DOS compatibility in Windows NT 3.x (or, rather, Turbo C for DOS compatibility in Microsoft C++ for Windows NT).
IIRC（我可能已经弄错了一些详细信息……），基本思想是：您将通过BIOS调用来获取hi和lo键盘的值，这意味着每个键都有一个16位值。为了使事情变得更简单，Turbo C提供了一个不错的调用，该调用会将键映射到当前（8位）代码页中的字符，因此 a 会给您一个回音。个字节， 0x61 。但是没有足够的空间来映射所有内容，因此在两个单独的调用中，未映射的特殊键如 VK_UP 将被返回，首先是hi字节 0xE0 ，然后是lo字节 0x50 。微软从Borland复制了该代码，以便更轻松地将代码移植到其编译器，然后再将代码从DOS / Win3.1移植到NT，这就是MSVCRT如今仍在做的事情，而Python只是包装了执行该功能的函数。
IIRC (and I've probably got a few of the details wrong…), the basic idea was this: You'd make a BIOS call to get hi and lo values for the keyboard, meaning every key had a 16-bit value. Turbo C, to make things easier, provided a nice call that would map keys to their character in the current (8-bit) codepage, so a would give you back a single byte, 0x61. But there wasn't enough room to map everything, so special keys like VK_UP would be returned unmapped, across two separate calls, first the hi byte 0xE0 and then the lo byte 0x50. Microsoft copied that from Borland to make it easier to port code to their compiler, and then to port code from DOS/Win3.1 to NT, and so that's what MSVCRT still does today, and Python is just wrapping the function that does that.
此答案提供了更多详细信息。
This answer gives some more details.
当然，在大多数Unix终端上，向上箭头也会发送一个字符序列，通常与该字符的光标向上显示控制序列相同，通常为 ESC ，然后 [，然后是 A 。但是人们不会期望像
Of course on most Unix terminals, the up arrow also send a sequence of characters, usually the same as the cursor-up display control sequence for that character, typically ESC, then [, then A. But people don't expect a single-character getch-like function to return a single value for every key on Unix, so nobody gets confused.
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