在Linux上使用Python监听全局键组合

Question

我刚写了一个小程序，可以每隔几分钟从Flickr上下载一张新的壁纸。

现在我想增加一个功能，让用户可以“喜欢”一张壁纸，这样喜欢的壁纸就会比不喜欢的壁纸出现得更频繁。

我想给这个功能设置一个全局的快捷键。

比如说：如果我按下ctrl+7，就能在Python中执行一个“喜欢”的功能。

有没有什么库可以实现这个功能？（比如在JavaScript中，有一个库可以用shortcut("ctrl-b", someFunction);来定义快捷键）

如果没有，那我该怎么做呢？我看到过这个类似的问题，但那是很久以前的了。

Answer 1

这里有一个更简洁的版本，它不仅解码了数据，还打印出了键的名称，而不仅仅是数字：

#!/usr/bin/env python2

# Captures all keyboard and mouse events, including modifiers
# Adapted from http://stackoverflow.com/questions/22367358/
# Requires python-xlib

from Xlib.display import Display
from Xlib import X, XK
from Xlib.ext import record
from Xlib.protocol import rq


class Listener:
  def __init__(self):
    self.disp = None
    self.keys_down = set()

  def keycode_to_key(self, keycode, state):
    i = 0
    if state & X.ShiftMask:
      i += 1
    if state & X.Mod1Mask:
      i += 2
    return self.disp.keycode_to_keysym(keycode, i)

  def key_to_string(self, key):
    keys = []
    for name in dir(XK):
      if name.startswith("XK_") and getattr(XK, name) == key:
        keys.append(name.lstrip("XK_").replace("_L", "").replace("_R", ""))
    if keys:
      return " or ".join(keys)
    return "[%d]" % key

  def keycode_to_string(self, keycode, state):
    return self.key_to_string(self.keycode_to_key(keycode, state))

  def mouse_to_string(self, code):
    if code == X.Button1:
      return "Button1"
    elif code == X.Button2:
      return "Button2"
    elif code == X.Button3:
      return "Button3"
    elif code == X.Button4:
      return "Button4"
    elif code == X.Button5:
      return "Button5"
    else:
      return "{%d}" % code

  def down(self, key):
    self.keys_down.add(key)
    self.print_keys()

  def up(self, key):
    if key in self.keys_down:
      self.keys_down.remove(key)
      self.print_keys()

  def print_keys(self):
    keys = list(self.keys_down)
    print "Currently pressed:", ", ".join(keys)

  def event_handler(self, reply):
    data = reply.data
    while data:
      event, data = rq.EventField(None).parse_binary_value(data, self.disp.display, None, None)
      if event.type == X.KeyPress:
        self.down(self.keycode_to_string(event.detail, event.state))
      elif event.type == X.KeyRelease:
        self.up(self.keycode_to_string(event.detail, event.state))
      elif event.type == X.ButtonPress:
        self.down(self.mouse_to_string(event.detail))
      elif event.type == X.ButtonRelease:
        self.up(self.mouse_to_string(event.detail))

  def run(self):
    self.disp = Display()
    XK.load_keysym_group('xf86')
    root = self.disp.screen().root
    ctx = self.disp.record_create_context(0,
                                          [record.AllClients],
                                          [{
                                            'core_requests': (0, 0),
                                            'core_replies': (0, 0),
                                            'ext_requests': (0, 0, 0, 0),
                                            'ext_replies': (0, 0, 0, 0),
                                            'delivered_events': (0, 0),
                                            'device_events': (X.KeyReleaseMask, X.ButtonReleaseMask),
                                            'errors': (0, 0),
                                            'client_started': False,
                                            'client_died': False,
                                          }])
    self.disp.record_enable_context(ctx, lambda reply: self.event_handler(reply))
    self.disp.record_free_context(ctx)
    while True:
      event = root.display.next_event()


if __name__ == "__main__":
  Listener().run()

输出结果看起来是这样的：

Currently pressed: Alt
Currently pressed:
Currently pressed: Alt
Currently pressed: Alt, Tab
Currently pressed: Alt
Currently pressed: Alt, Tab
Currently pressed: Alt
Currently pressed: Alt, Tab
Currently pressed: Alt
Currently pressed: Alt, Tab
Currently pressed: Alt
Currently pressed: Alt, Tab
Currently pressed: Alt
Currently pressed:
Currently pressed: Control
Currently pressed: Control, a
Currently pressed: Control
Currently pressed: Control, Shift
Currently pressed: Control, Shift, A
Currently pressed: Control, Shift

Answer 2

对于想看看我最终使用的代码的人，我在这里做了一个小的代码片段 就在这里。

每台电脑的按键代码可能会有些不同。另外，我快速写的这个按键监听类并没有考虑到所有可能出现的问题。不过，对我来说，它的效果还不错。

Answer 3

我不知道有没有专门设计用来扩展的库。不过，正如你链接中提到的，pykeylogger的后台给出了一个如何实现的例子，但看起来有点复杂，不太适合你的需求。

pykeylogger使用python-xlib模块来捕捉X显示器上的按键。有人已经在pastebin上创建了一个更简单的例子，下面是从那里复制过来的源代码。

from Xlib.display import Display
from Xlib import X
from Xlib.ext import record
from Xlib.protocol import rq

disp = None

def handler(reply):
    """ This function is called when a xlib event is fired """
    data = reply.data
    while len(data):
        event, data = rq.EventField(None).parse_binary_value(data, disp.display, None, None)

        # KEYCODE IS FOUND USERING event.detail
        print(event.detail)

        if event.type == X.KeyPress:
            # BUTTON PRESSED
            print("pressed")
        elif event.type == X.KeyRelease:
            # BUTTON RELEASED
            print("released")

# get current display
disp = Display()
root = disp.screen().root

# Monitor keypress and button press
ctx = disp.record_create_context(
            0,
            [record.AllClients],
            [{
                    'core_requests': (0, 0),
                    'core_replies': (0, 0),
                    'ext_requests': (0, 0, 0, 0),
                    'ext_replies': (0, 0, 0, 0),
                    'delivered_events': (0, 0),
                    'device_events': (X.KeyReleaseMask, X.ButtonReleaseMask),
                    'errors': (0, 0),
                    'client_started': False,
                    'client_died': False,
            }])
disp.record_enable_context(ctx, handler)
disp.record_free_context(ctx)

while 1:
    # Infinite wait, doesn't do anything as no events are grabbed
    event = root.display.next_event()

你需要扩展处理程序，以满足你的需求，不仅仅是打印到屏幕上，然后把它放到一个单独的线程中。

另一个（比较麻烦的）选择是直接监听键盘，而不依赖外部库或X会话。在Linux中，一切都是文件，你的键盘输入会在/dev/input中，你可以把它当作文件来读取，比如open('/dev/input/event2', 'rb')，在后台进行。这种方法不太推荐，因为它需要更高的权限，还要搞清楚哪个设备是键盘，然后自己创建按键映射。我只是想让你知道如果有必要的话，这种方法是可行的。

补充：我还发现了使用Python gtk3在X上实现全局按键绑定，看起来有更多的例子可以参考。