check if key pressed is alphanumeric

also happens to ignore unknown key presses

CARDPUTER CircuitPython/keyboard.py

         }
         self.special={
             "0xa":"\n", "0x8":"BACKSP", "0x20":" ", "0x3b":"UP", "0x2e":"DOWN", "0x2c":"LEFT", "0x2f":"RIGHT", "0x10d":"OPTD",
-            "0x4":"CTRLD", "0x13":"CTRLS", "0x9":"    ", "0x60":"ESC"
+            "0x4":"CTRLD", "0x13":"CTRLS", "0x9":"    ", "0x60":"ESC", "0xf":"CTRLO"
         }
 
     def scan(self):
         if key:
             return key
         else:
-            return "UNKNOWN "+code
+            return "UNKNOWN "+code
+
+    def is_alphanumeric(self, key):
+        if key in self.special.values() or key in self.chars.values():
+            return False
+        else:
+            return True