Update nditracker.py error messages

sksurgerynditracker/nditracker.py

@@ -18,6 +18,15 @@
 from sksurgerynditracker.serial_utils.com_ports import \
         fix_com_port_greater_than_9
 
+SERIAL_CONNECTION_ERRMSG = """
+Please check the following:\n
+\t1) Is an NDI device connected to your computer?\n
+\t2) Is the NDI device switched on?\n
+\t3) Do you have sufficient privilege to connect to
+the device? (e.g. on Linux are you part of the "dialout"
+group?)'
+"""
+
 @contextlib.contextmanager
 def _open_logging(verbose):
     """
@@ -65,30 +74,31 @@ def _get_serial_port_name(configuration):
                       " Result: ", result, file=fileout)
                 if result == ndicapy.NDI_OKAY:
                     break
+        else:
+                raise IOError('Could not find any NDI device in '
+                    f'{ports_to_probe} serial port candidates checked. '
+                    + SERIAL_CONNECTION_ERRMSG)
+
         else:
             if isinstance(serial_port, int):
                 if serial_port < len(serial_ports):
                     name = serial_ports[serial_port].device
                     result = ndicapy.ndiProbe(name)
                     print("Probing port: ", serial_port, " got name: ", name,
                           " Result: ", result, file=fileout)
+                else:
+                    raise IOError(f'Could not connect to serial port {serial_port} '
+                        f'as there are only {len(serial_ports)} ports available'
+                        + SERIAL_CONNECTION_ERRMSG)
+
             if isinstance(serial_port, str):
                 name = serial_port
                 result = ndicapy.ndiProbe(name)
                 print("Probing port: ", name,
                       " Result: ", result, file=fileout)
-
-        if result != ndicapy.NDI_OKAY:
-            raise IOError(
-                'Could not find any NDI device in '
-                f'{ports_to_probe} serial port candidates checked. '
-                'Please check the following:\n'
-                '\t1) Is an NDI device connected to your computer?\n'
-                '\t2) Is the NDI device switched on?\n'
-                '\t3) Do you have sufficient privilege to connect to '
-                'the device? (e.g. on Linux are you part of the "dialout" '
-                'group?)')
-
+            if result != ndicapy.NDI_OKAY:
+                raise IOError(f'Could not connect to an NDI device on the chosen port, {serial_port}.'
+                    + SERIAL_CONNECTION_ERRMSG)
         return name