Removed LookAndFeel capability for Mac platform. The function does nothing if sys.platform == 'darwin'. Added warning messages trying to help user when Finalize is not called when it should be. Removed candidate function names PrepareForUpdate and PreRead. Ended up using Finalize as final function name

PySimpleGUI.py

@@ -1233,6 +1233,9 @@ class Canvas(Element):
 
     @property
     def TKCanvas(self):
+        if self._TKCanvas is None:
+            print('*** Did you forget to call Finalize()? Your code should look something like: ***')
+            print('*** form = sg.FlexForm("My Form").Layout(layout).Finalize() ***')
         return self._TKCanvas
 
 
@@ -1308,6 +1311,9 @@ class Graph(Element):
 
     @property
     def TKCanvas(self):
+        if self._TKCanvas2 is None:
+            print('*** Did you forget to call Finalize()? Your code should look something like: ***')
+            print('*** form = sg.FlexForm("My Form").Layout(layout).Finalize() ***')
         return self._TKCanvas2
 
     def __del__(self):
@@ -2015,10 +2021,6 @@ class FlexForm:
             # return None, None
         return self
 
-    # Another name for ReadNonBlocking.
-    PrepareForUpdate = ReadNonBlocking
-    # Finalize = ReadNonBlocking
-    PreRead = ReadNonBlocking
 
 
     def Refresh(self):
@@ -3976,6 +3978,10 @@ def SetOptions(icon=None, button_color=None, element_size=(None,None), button_el
 # of the elements.                                           #
 ##############################################################
 def ChangeLookAndFeel(index):
+    if sys.platform == 'darwin':
+        print('*** Changing look and feel is not supported on Mac platform ***')
+        return
+
     # look and feel table
     look_and_feel =  {'SystemDefault': {'BACKGROUND' : COLOR_SYSTEM_DEFAULT, 'TEXT': COLOR_SYSTEM_DEFAULT, 'INPUT': COLOR_SYSTEM_DEFAULT,'TEXT_INPUT' : COLOR_SYSTEM_DEFAULT, 'SCROLL': COLOR_SYSTEM_DEFAULT, 'BUTTON': OFFICIAL_PYSIMPLEGUI_BUTTON_COLOR, 'PROGRESS': COLOR_SYSTEM_DEFAULT, 'BORDER': 1,'SLIDER_DEPTH':1, 'PROGRESS_DEPTH':0},