Fix #289

Tweak the second keyboard robot recipe so it detects keyboards and
doesn't throw exceptions on unknown keys. Also add a note to the recipe
that it won't work over remote connections like SSH.

docs/examples/robot_keyboard_2.py

@@ -3,8 +3,23 @@ from evdev import InputDevice, list_devices, ecodes
 
 robot = Robot(left=(4, 14), right=(17, 18))
 
+# Get the list of available input devices
 devices = [InputDevice(device) for device in list_devices()]
-keyboard = devices[0]  # this may vary
+# Filter out everything that's not a keyboard. Keyboards are defined as any
+# device which has keys, and which specifically has keys 1..31 (roughly Esc,
+# the numeric keys, the first row of QWERTY plus a few more) and which does
+# *not* have key 0 (reserved)
+must_have = {i for i in range(1, 32)}
+must_not_have = {0}
+devices = [
+    device
+    for device in devices
+    for keys in (set(device.capabilities().get(ecodes.EV_KEY, [])),)
+    if must_have.issubset(keys)
+    and must_not_have.isdisjoint(keys)
+]
+# Pick the first keyboard
+keyboard = devices[0]
 
 keypress_actions = {
     ecodes.KEY_UP: robot.forward,
@@ -14,7 +29,7 @@ keypress_actions = {
 }
 
 for event in keyboard.read_loop():
-    if event.type == ecodes.EV_KEY:
+    if event.type == ecodes.EV_KEY and event.code in keypress_actions:
         if event.value == 1:  # key down
             keypress_actions[event.code]()
         if event.value == 0:  # key up