Safe handling of dictionary lookup when decoding DTC

tool/modules/dcm.py

@@ -69,9 +69,10 @@
     0x7F: 'serviceNotSupportedInActiveSession'
 }
 
+
 def dcm_dtc(args):
     """
-    Fetches the Diagnostic Trouble Codes from a supported service (Mode $03)
+    Fetches and prints the Diagnostic Trouble Codes from a supported service (Mode $03)
 
     :param args: A namespace containing src, dst and clear
     """
@@ -86,25 +87,25 @@ def decode_dtc(msg):
             return
 
         def dtc_type(x):
-          return {
-            0: 'P',
-            1: 'B',
-            2: 'C',
-            3: 'U',
-          }[x]
+            return {
+                0: 'P',
+                1: 'B',
+                2: 'C',
+                3: 'U',
+            }.get(x, "?")
 
-        dtc_msg = dtc_type(msg.data[3] & 0xF0 >> 4) + format(msg.data[3] & 0x0F, '01x') + format(msg.data[4], '02x')
-        print("DTC: {0}\n".format(dtc_msg))
-        return decode_dtc
+        dtc_type_char = dtc_type(msg.data[3] & 0xF0 >> 4)
+        print("DTC: {0}{1:01x}{2:02x}\n".format(dtc_type_char, msg.data[3] & 0x0F, msg.data[4]))
 
     with CanActions(arb_id=send_arb_id) as can_wrap:
         if clear:
-          can_wrap.send([0x01, 0x04])
-          print("Cleared DTCs and reset MIL")
+            can_wrap.send([0x01, 0x04])
+            print("Cleared DTCs and reset MIL")
         else:
-          print("Fetching Diagnostic Trouble Codes")
-          can_wrap.send_single_message_with_callback([0x01, 0x03], decode_dtc)
-          time.sleep(1)
+            print("Fetching Diagnostic Trouble Codes")
+            can_wrap.send_single_message_with_callback([0x01, 0x03], decode_dtc)
+            time.sleep(1)
+
 
 def dcm_discovery(args):
     """