Detect plugins without Python 3.x support and warn user.

To allow users to sort out their plugins before EDMC itself moves to
Python 3.x warn them if any of their enabled, non-stock, plugins do not
have a plugin_start3() method.

  * If any are found without support there's a popup triggered at the
    end of AppWindow initialisation.
  * Then the user can check Settings > Plugins to see a list of the
    plugins without Python 3.x support.

EDMarketConnector.py

@@ -299,6 +299,13 @@ class AppWindow:
 
         self.postprefs(False)	# Companion login happens in callback from monitor
 
+        if len(plug.PLUGINS_not_py3):
+            import tkMessageBox
+            tkMessageBox.showinfo('Plugins Without Python 3.x Support',
+                    "One or more of your enabled plugins do not yet have support for Python 3.x.  Please see the list on the 'Plugins' tab of 'File' > 'Settings'.  You should check if there is an updated version available, else alert the developer that they will need to update the code when EDMC moves to Python 3.x"
+            )
+
+
     # callback after the Preferences dialog is applied
     def postprefs(self, dologin=True):
         self.prefsdialog = None

plug.py

@@ -65,6 +65,7 @@ GuiFocusCodex = 11
 
 # List of loaded Plugins
 PLUGINS = []
+PLUGINS_not_py3 = []
 
 # For asynchronous error display
 last_error = {
@@ -195,6 +196,14 @@ def load_plugins(master):
                 print_exc()
     PLUGINS.extend(sorted(found, key = lambda p: operator.attrgetter('name')(p).lower()))
 
+    #########################################################
+    # Detect plugins that aren't yet ready for Python 3.x
+    #########################################################
+    for p in PLUGINS:
+        if p.module and p.folder and not p._get_func('plugin_start3'):
+            PLUGINS_not_py3.append(p)
+    #########################################################
+
     imp.release_lock()
 
 def provides(fn_name):

prefs.py

@@ -273,6 +273,18 @@ class PreferencesDialog(tk.Toplevel):
                     label = nb.Label(plugsframe, text='%s (%s)' % (plugin.folder, plugin.name))
                 label.grid(columnspan=2, padx=PADX*2, sticky=tk.W)
 
+        ############################################################
+        # Show which plugins don't have Python 3.x support
+        ############################################################
+        if len(plug.PLUGINS_not_py3):
+            ttk.Separator(plugsframe, orient=tk.HORIZONTAL).grid(columnspan=3, padx=PADX, pady=PADY * 8, sticky=tk.EW)
+            nb.Label(plugsframe, text=_('Plugins Without Python 3.x Support')+':').grid(padx=PADX, sticky=tk.W)	# List of plugins in settings
+            for plugin in plug.PLUGINS_not_py3:
+                if plugin.folder: # 'system' ones have this set to None to suppress listing in Plugins prefs tab
+                    nb.Label(plugsframe, text=plugin.name).grid(columnspan=2, padx=PADX*2, sticky=tk.W)
+
+        ############################################################
+
         disabled_plugins = [x for x in plug.PLUGINS if x.folder and not x.module]
         if len(disabled_plugins):
             ttk.Separator(plugsframe, orient=tk.HORIZONTAL).grid(columnspan=3, padx=PADX, pady=PADY * 8, sticky=tk.EW)