如何使用evdev从Python中的HID设备获取字符串？

Question

我是python新手，但对HID设备和evdev有经验。我有一个二维条码扫描仪接口作为隐藏设备。目标是从二维码中获取字符串。我能够识别Linux中的扫描仪，甚至可以在/dev/input中找到它的位置。

我找到了evdev并用我的扫描仪实现了下面的示例。这只是他们网站上的默认代码。它会读取值，但会打印长事件代码，其中包含向下和向上。我看不出一个简单的方法把这个变成字符串。我只想从Python中的HID扫描器读取一个字符串。任何帮助或指导都将不胜感激（也许evdev不是答案）。

下面是我当前的python代码和一些示例输出：

from evdev import *
dev = InputDevice('/dev/input/event1')

print(dev)

for event in dev.read_loop():
    if event.type == ecodes.EV_KEY:
        print(categorize(event))

下面是一些条形码的输出：

key event at 1383327570.147000, 2 (KEY_1), down
key event at 1383327570.147990, 2 (KEY_1), up
key event at 1383327570.148997, 3 (KEY_2), down
key event at 1383327570.150010, 3 (KEY_2), up
key event at 1383327570.151009, 29 (KEY_LEFTCTRL), down
key event at 1383327570.151009, 42 (KEY_LEFTSHIFT), down
key event at 1383327570.152017, 36 (KEY_J), down
key event at 1383327570.153005, 36 (KEY_J), up
key event at 1383327570.154004, 29 (KEY_LEFTCTRL), up
key event at 1383327570.155005, 32 (KEY_D), down
key event at 1383327570.155993, 32 (KEY_D), up
key event at 1383327570.157002, 48 (KEY_B), down
key event at 1383327570.158015, 48 (KEY_B), up
key event at 1383327570.158997, 48 (KEY_B), down
key event at 1383327570.282002, 18 (KEY_E), up
key event at 1383327570.283004, 49 (KEY_N), down
key event at 1383327570.284005, 49 (KEY_N), up
key event at 1383327570.284968, 18 (KEY_E), down

非常感谢！

Answer 1

这里缺少一个转换步骤。您的输出格式已经很不错了，所以我将帮助您进一步分解它：

             Timestamp        , scancode, keycode, keystate
key event at 1383327570.147000, 2         (KEY_1), down
key event at 1383327570.147990, 2         (KEY_1), up

要对此有任何有用的理解，您需要做两件事：

1. 仅按筛选器侦听特定类型（down=1，Up=0）的键状态的键关闭类型事件
2. 将扫描码转换成一个ASCII码，它可以随设备的不同而变化，也可以随映射到系统的方式而变化！

不过，有一个简单的方法来绘制它们。使用在线服务生成包含所有可用字符的已知条形码，然后扫描该条形码并将输出的每个扫描码映射到扫描仪的正确字母/号码。您可以使用以下稍微修改过的代码来更好地控制输出：

import evdev
from evdev import InputDevice, categorize  # import * is evil :)
dev = InputDevice('/dev/input/event1')

# Provided as an example taken from my own keyboard attached to a Centos 6 box:
scancodes = {
    # Scancode: ASCIICode
    0: None, 1: u'ESC', 2: u'1', 3: u'2', 4: u'3', 5: u'4', 6: u'5', 7: u'6', 8: u'7', 9: u'8',
    10: u'9', 11: u'0', 12: u'-', 13: u'=', 14: u'BKSP', 15: u'TAB', 16: u'Q', 17: u'W', 18: u'E', 19: u'R',
    20: u'T', 21: u'Y', 22: u'U', 23: u'I', 24: u'O', 25: u'P', 26: u'[', 27: u']', 28: u'CRLF', 29: u'LCTRL',
    30: u'A', 31: u'S', 32: u'D', 33: u'F', 34: u'G', 35: u'H', 36: u'J', 37: u'K', 38: u'L', 39: u';',
    40: u'"', 41: u'`', 42: u'LSHFT', 43: u'\\', 44: u'Z', 45: u'X', 46: u'C', 47: u'V', 48: u'B', 49: u'N',
    50: u'M', 51: u',', 52: u'.', 53: u'/', 54: u'RSHFT', 56: u'LALT', 100: u'RALT'
}
for event in dev.read_loop():
    if event.type == evdev.ecodes.EV_KEY:
        data = evdev.categorize(event)  # Save the event temporarily to introspect it
        if data.keystate == 1:  # Down events only
            key_lookup = scancodes.get(data.scancode) or u'UNKNOWN:{}'.format(data.scancode)  # Lookup or return UNKNOWN:XX
            print u'You Pressed the {} key!'.format(key_lookup)  # Print it all out!

下面是这个脚本的一些示例输出

You Pressed the A key!
You Pressed the B key!
You Pressed the C key!
You Pressed the UNKNOWN:99 key!

一旦你在线生成一些条码，你就会知道哪个扫描码被映射到哪个值！建立你自己的表和利润！

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