device_server.serve_devices: copy devices to prevent change on caller (#211)

This commit has serve_devices make a deepcopy of the devices argument
so that in case we need to make changes to it, we don't modify the
stuff in the caller.  This commit reverts ef280c3 which was
another fix for this issue.

The way we support floating devices requires that we inject the index
value on the device configuration.  However, we don't want that to
propagate to the caller which may be reusing that configuration (and
it kinda does it when device configuration is not specified see
discussion on #212).

Author: carandraug

microscope/device_server.py

@@ -35,6 +35,7 @@
 """
 
 import argparse
+import copy
 import importlib.machinery
 import importlib.util
 import logging
@@ -81,7 +82,7 @@ def device(
     cls: typing.Callable,
     host: str,
     port: int,
-    conf: typing.Mapping[str, typing.Any] = None,
+    conf: typing.Mapping[str, typing.Any] = {},
     uid: typing.Optional[str] = None,
 ):
     """Define devices and where to serve them.
@@ -119,8 +120,6 @@ def construct_devices() -> typing.Dict[str, Device]:
         ]
 
     """
-    if conf is None:
-        conf = {}
     if not callable(cls):
         raise TypeError("cls must be a callable")
     elif isinstance(cls, type):
@@ -392,6 +391,12 @@ def run(self):
 
 
 def serve_devices(devices, options: DeviceServerOptions, exit_event=None):
+    # We make changes to `devices` (would be great if we didn't had
+    # to) so make a a copy of it because we don't want to make those
+    # changes on the caller.  See original issue on #211 and PRs #212
+    # and #217 (most discussion happens on #212).
+    devices = copy.deepcopy(devices)
+
     root_logger = logging.getLogger()
 
     log_handler = RotatingFileHandler("__MAIN__.log")