DeviceServer: remove count arg; expect index in kwargs instead (issue #84)

Instead of having to explain the count/index special case in both
serve_devices() and DeviceServer, limit it to serve_devices() by
adding it to the device constructor arguments as soon as it is
generated.

Author: carandraug

microscope/deviceserver.py

@@ -93,14 +93,12 @@ def filter(self, record):
 
 
 class DeviceServer(multiprocessing.Process):
-    def __init__(self, device_def, id_to_host, id_to_port, count=0,
-                 exit_event=None):
+    def __init__(self, device_def, id_to_host, id_to_port, exit_event=None):
         """Initialise a device and serve at host/port according to its id.
 
         :param device_def: definition of the device
         :param id_to_host: host or mapping of device identifiers to hostname
         :param id_to_port: map or mapping of device identifiers to port number
-        :param count:      this is the countth process serving this class
         :param exit_event: a shared event to signal that the process
             should quit.
         """
@@ -114,17 +112,14 @@ def __init__(self, device_def, id_to_host, id_to_port, count=0,
         self.exit_event = exit_event
         super(DeviceServer, self).__init__()
         self.daemon = True
-        # Some SDKs need an index to access more than one device.
-        self.count = count
 
     def clone(self):
         """Create new instance with same settings.
 
         This is useful to restart a device server.
         """
         return DeviceServer(self._device_def, self._id_to_host,
-                            self._id_to_port, exit_event=self.exit_event,
-                            count=self.count)
+                            self._id_to_port, exit_event=self.exit_event)
 
     def run(self):
         logger = logging.getLogger(self._device_def['cls'].__name__)
@@ -148,7 +143,7 @@ def run(self):
         for def_key in ['cls', 'host', 'port', 'uid']:
             init_kwargs.pop(def_key)
 
-        self._device = self._device_def['cls'](index=self.count, **init_kwargs)
+        self._device = self._device_def['cls'](**init_kwargs)
         while not self.exit_event.is_set():
             try:
                 self._device.initialize()
@@ -263,9 +258,9 @@ def term_func(sig, frame):
             uid_to_port = None
 
         for dev in devs:
-            servers.append(DeviceServer(dev,
-                                        uid_to_host, uid_to_port,
-                                        exit_event=exit_event, count=count))
+            dev['index'] = count
+            servers.append(DeviceServer(dev, uid_to_host, uid_to_port,
+                                        exit_event=exit_event))
             servers[-1].start()
             count += 1