Type annotations: use __future__.annotations flag for backward and fo…

…rward compatibility. Re #155.

Annotate functions and variables to make it clear as to what is what and what type it is. As a first step, use __future__.annotations import to guarantee forward and backward compatibility (to be removed in Python 3.10 version). This is better than importing uppercase versions of containers from typing module as these are deprecated in Python 3.9.
The overall type annotations are guided by Mypy, a static type checker.

addon/appModules/splcreator.py

@@ -4,6 +4,9 @@
 
 # Basic support for StationPlaylist Creator.
 
+# #155 (21.03): remove __future__ import when NVDA runs under Python 3.10.
+from __future__ import annotations
+from typing import Any
 import appModuleHandler
 import addonHandler
 import scriptHandler

addon/appModules/splengine/encoders.py

@@ -2,6 +2,8 @@
 # Copyright 2015-2021 Joseph Lee, released under GPL.
 # Split from main global plugin in 2015, transferred to SPL Engine app module in 2020.
 
+# #155 (21.03): remove __future__ import when NVDA runs under Python 3.10.
+from __future__ import annotations
 import threading
 import time
 import os

addon/appModules/splremotevt.py

@@ -5,6 +5,9 @@
 # Basic support for StationPlaylist Remote VT Client.
 # Borrows heavily from creator as the user interface is quite similar with changes specific to VT Client.
 
+# #155 (21.03): remove __future__ import when NVDA runs under Python 3.10.
+from __future__ import annotations
+from typing import Any
 import addonHandler
 import globalVars
 import ui

addon/appModules/splstudio/__init__.py

@@ -12,6 +12,9 @@
 
 # Minimum version: SPL 5.30, NVDA 2020.3.
 
+# #155 (21.03): remove __future__ import when NVDA runs under Python 3.10.
+from __future__ import annotations
+from typing import Any
 from functools import wraps
 import os
 import time

addon/appModules/splstudio/splconfig.py

@@ -6,6 +6,9 @@
 # For UI surrounding this module, see splconfui module.
 # For the add-on settings specification, see splconfspec module.
 
+# #155 (21.03): remove __future__ import when NVDA runs under Python 3.10.
+from __future__ import annotations
+from typing import Optional, Any
 import os
 import pickle
 from collections import ChainMap