diff --git a/Lib/idlelib/configdialog.py b/Lib/idlelib/configdialog.py
index 4a25846..8409227 100644
--- a/Lib/idlelib/configdialog.py
+++ b/Lib/idlelib/configdialog.py
@@ -28,10 +28,16 @@
 from idlelib.tabbedpages import TabbedPageSet
 from idlelib.textview import view_text
 
+
 class ConfigDialog(Toplevel):
+    """Config dialog for IDLE.
+    """
 
     def __init__(self, parent, title='', _htest=False, _utest=False):
-        """
+        """Show the tabbed dialog for user configuration.
+
+        parent - parent of this dialog
+        title - string which is the title of this popup dialog
         _htest - bool, change box location when running htest
         _utest - bool, don't wait_window when running unittest
         """
@@ -46,9 +52,9 @@
         x = parent.winfo_rootx() + 20
         y = parent.winfo_rooty() + (30 if not _htest else 150)
         self.geometry(f'+{x}+{y}')
-        #Theme Elements. Each theme element key is its display name.
-        #The first value of the tuple is the sample area tag name.
-        #The second value is the display name list sort index.
+        # Each theme element key is its display name.
+        # The first value of the tuple is the sample area tag name.
+        # The second value is the display name list sort index.
         self.theme_elements={
             'Normal Text': ('normal', '00'),
             'Python Keywords': ('keyword', '01'),
@@ -65,25 +71,27 @@
             'Shell Stdout Text': ('stdout', '12'),
             'Shell Stderr Text': ('stderr', '13'),
             }
-        self.reset_changed_items() #load initial values in changed items dict
+        self.reset_changed_items()  # Initialize changed_items dict.
         self.create_widgets()
         self.resizable(height=FALSE, width=FALSE)
         self.transient(parent)
         self.grab_set()
         self.protocol("WM_DELETE_WINDOW", self.cancel)
         self.tab_pages.focus_set()
-        #key bindings for this dialog
-        #self.bind('<Escape>', self.Cancel) #dismiss dialog, no save
-        #self.bind('<Alt-a>', self.Apply) #apply changes, save
-        #self.bind('<F1>', self.Help) #context help
+        # XXX Decide whether to keep or delete these key bindings.
+        # Key bindings for this dialog.
+        # self.bind('<Escape>', self.Cancel) #dismiss dialog, no save
+        # self.bind('<Alt-a>', self.Apply) #apply changes, save
+        # self.bind('<F1>', self.Help) #context help
         self.load_configs()
-        self.attach_var_callbacks() #avoid callbacks during load_configs
+        self.attach_var_callbacks()  # Avoid callbacks during load_configs.
 
         if not _utest:
             self.wm_deiconify()
             self.wait_window()
 
     def create_widgets(self):
+        "Create and place widgets for tabbed dialog."
         self.tab_pages = TabbedPageSet(self,
                 page_names=['Fonts/Tabs', 'Highlighting', 'Keys', 'General',
                             'Extensions'])
@@ -96,9 +104,10 @@
         self.create_action_buttons().pack(side=BOTTOM)
 
     def create_action_buttons(self):
+        "Return frame of action buttons for dialog."
         if macosx.isAquaTk():
             # Changing the default padding on OSX results in unreadable
-            # text in the buttons
+            # text in the buttons.
             padding_args = {}
         else:
             padding_args = {'padx':6, 'pady':3}
@@ -111,12 +120,21 @@
             ('Help', self.help)):
             Button(buttons, text=txt, command=cmd, takefocus=FALSE,
                    **padding_args).pack(side=LEFT, padx=5)
-        # add space above buttons
+        # Add space above buttons.
         Frame(outer, height=2, borderwidth=0).pack(side=TOP)
         buttons.pack(side=BOTTOM)
         return outer
 
     def create_page_font_tab(self):
+        """Return frame of widgets for Font/Tabs tab.
+
+        Configuration attributes:
+            font_size: Font size.
+            font_bold: Select font bold or not.
+            font_name: Font face.
+            space_num: Indentation width.
+            edit_font: Font widget with default font name, size, and weight.
+        """
         parent = self.parent
         self.font_size = StringVar(parent)
         self.font_bold = BooleanVar(parent)
@@ -185,11 +203,22 @@
         return frame
 
     def create_page_highlight(self):
+        """Return frame of widgets for Highlighting tab.
+
+        Configuration attributes:
+            builtin_theme: Menu variable for built-in theme.
+            custom_theme: Menu variable for custom theme.
+            fg_bg_toggle: Toggle for foreground/background color.
+            colour: Color of selected target.
+            is_builtin_theme: Selector for built-in or custom theme.
+            highlight_target: Menu variable for the highlight tag target.
+        """
         parent = self.parent
         self.builtin_theme = StringVar(parent)
         self.custom_theme = StringVar(parent)
         self.fg_bg_toggle = BooleanVar(parent)
         self.colour = StringVar(parent)
+        # XXX - font_name is defined in create_page_font_tab.  Needed here too?
         self.font_name = StringVar(parent)
         self.is_builtin_theme = BooleanVar(parent)
         self.highlight_target = StringVar(parent)
@@ -296,7 +325,16 @@
         return frame
 
     def create_page_keys(self):
+        """Return frame of widgets for Keys tab.
+
+        Configuration attributes:
+            builtin_keys: Menu variable for built-in keybindings.
+            custom_keys: Menu variable for custom keybindings.
+            are_keys_builtin: Selector for built-in or custom keybindings.
+            keybinding: Action/key bindings.
+        """
         parent = self.parent
+        # XXX - binding_target isn't used.
         self.binding_target = StringVar(parent)
         self.builtin_keys = StringVar(parent)
         self.custom_keys = StringVar(parent)
@@ -375,12 +413,23 @@
         return frame
 
     def create_page_general(self):
+        """Return frame of widgets for General tab.
+
+        Configuration attributes:
+            win_width: Initial window width in characters.
+            win_height: Initial window height in characters.
+            startup_edit: Selector for opening in editor or shell mode.
+            autosave: Selector for save prompt popup when using Run.
+            encoding: ?
+        """
         parent = self.parent
         self.win_width = StringVar(parent)
         self.win_height = StringVar(parent)
         self.startup_edit = IntVar(parent)
         self.autosave = IntVar(parent)
+        # XXX - encoding isn't on the screen to be set, but is saved to config.
         self.encoding = StringVar(parent)
+        # XXX - user_help_browser and help_browser aren't used.
         self.user_help_browser = BooleanVar(parent)
         self.help_browser = StringVar(parent)
 
@@ -471,6 +520,7 @@
         return frame
 
     def attach_var_callbacks(self):
+        "Attach callbacks to variables that can be changed."
         self.font_size.trace_add('write', self.var_changed_font)
         self.font_name.trace_add('write', self.var_changed_font)
         self.font_bold.trace_add('write', self.var_changed_font)
@@ -502,10 +552,12 @@
             var.trace_remove('write', var.trace_info()[0][1])
 
     def var_changed_font(self, *params):
-        '''When one font attribute changes, save them all, as they are
+        """Store changes to font attributes.
+
+        When one font attribute changes, save them all, as they are
         not independent from each other. In particular, when we are
         overriding the default font, we need to write out everything.
-        '''
+        """
         value = self.font_name.get()
         self.add_changed_item('main', 'EditorWindow', 'font', value)
         value = self.font_size.get()
@@ -514,13 +566,20 @@
         self.add_changed_item('main', 'EditorWindow', 'font-bold', value)
 
     def var_changed_space_num(self, *params):
+        "Store change to indentation size."
         value = self.space_num.get()
         self.add_changed_item('main', 'Indent', 'num-spaces', value)
 
     def var_changed_colour(self, *params):
+        "Process change to color choice."
         self.on_new_colour_set()
 
     def var_changed_builtin_theme(self, *params):
+        """Process new builtin theme selection.
+
+        Add the changed theme's name to the changed_items and recreate
+        the sample with the values from the selected theme.
+        """
         old_themes = ('IDLE Classic', 'IDLE New')
         value = self.builtin_theme.get()
         if value not in old_themes:
@@ -536,12 +595,22 @@
         self.paint_theme_sample()
 
     def var_changed_custom_theme(self, *params):
+        """Process new custom theme selection.
+
+        If a new custom theme is selected, add the name to the
+        changed_items and apply the theme to the sample.
+        """
         value = self.custom_theme.get()
         if value != '- no custom themes -':
             self.add_changed_item('main', 'Theme', 'name', value)
             self.paint_theme_sample()
 
     def var_changed_is_builtin_theme(self, *params):
+        """Process toggle between builtin and custom theme.
+
+        Update the default toggle value and apply the newly
+        selected theme type.
+        """
         value = self.is_builtin_theme.get()
         self.add_changed_item('main', 'Theme', 'default', value)
         if value:
@@ -550,21 +619,23 @@
             self.var_changed_custom_theme()
 
     def var_changed_highlight_target(self, *params):
+        "Process selection of new target tag for highlighting."
         self.set_highlight_target()
 
     def var_changed_keybinding(self, *params):
+        "Store change to a keybinding."
         value = self.keybinding.get()
         key_set = self.custom_keys.get()
         event = self.list_bindings.get(ANCHOR).split()[0]
         if idleConf.IsCoreBinding(event):
-            #this is a core keybinding
             self.add_changed_item('keys', key_set, event, value)
-        else: #this is an extension key binding
+        else:  # Event is an extension binding.
             ext_name = idleConf.GetExtnNameForEvent(event)
             ext_keybind_section = ext_name + '_cfgBindings'
             self.add_changed_item('extensions', ext_keybind_section, event, value)
 
     def var_changed_builtin_keys(self, *params):
+        "Process selection of builtin key set."
         old_keys = (
             'IDLE Classic Windows',
             'IDLE Classic Unix',
@@ -585,12 +656,14 @@
         self.load_keys_list(value)
 
     def var_changed_custom_keys(self, *params):
+        "Process selection of custom key set."
         value = self.custom_keys.get()
         if value != '- no custom keys -':
             self.add_changed_item('main', 'Keys', 'name', value)
             self.load_keys_list(value)
 
     def var_changed_are_keys_builtin(self, *params):
+        "Process toggle between builtin key set and custom key set."
         value = self.are_keys_builtin.get()
         self.add_changed_item('main', 'Keys', 'default', value)
         if value:
@@ -599,41 +672,51 @@
             self.var_changed_custom_keys()
 
     def var_changed_win_width(self, *params):
+        "Store change to window width."
         value = self.win_width.get()
         self.add_changed_item('main', 'EditorWindow', 'width', value)
 
     def var_changed_win_height(self, *params):
+        "Store change to window height."
         value = self.win_height.get()
         self.add_changed_item('main', 'EditorWindow', 'height', value)
 
     def var_changed_startup_edit(self, *params):
+        "Store change to toggle for starting IDLE in the editor or shell."
         value = self.startup_edit.get()
         self.add_changed_item('main', 'General', 'editor-on-startup', value)
 
     def var_changed_autosave(self, *params):
+        "Store change to autosave."
         value = self.autosave.get()
         self.add_changed_item('main', 'General', 'autosave', value)
 
     def var_changed_encoding(self, *params):
+        "Store change to encoding."
         value = self.encoding.get()
         self.add_changed_item('main', 'EditorWindow', 'encoding', value)
 
     def reset_changed_items(self):
-        #When any config item is changed in this dialog, an entry
-        #should be made in the relevant section (config type) of this
-        #dictionary. The key should be the config file section name and the
-        #value a dictionary, whose key:value pairs are item=value pairs for
-        #that config file section.
+        """Reset dictionary containing the items changed on each tab.
+
+        When any config item is changed in this dialog, an entry
+        should be made in the relevant section (config type) of this
+        dictionary. The key should be the config file section name and the
+        value a dictionary, whose key:value pairs are item=value pairs for
+        that config file section.
+        """
         self.changed_items = {'main':{}, 'highlight':{}, 'keys':{},
                              'extensions':{}}
 
     def add_changed_item(self, typ, section, item, value):
-        value = str(value) #make sure we use a string
+        "Add item/value pair to changed items dictionary for typ and section."
+        value = str(value)  # Make sure we use a string.
         if section not in self.changed_items[typ]:
             self.changed_items[typ][section] = {}
         self.changed_items[typ][section][item] = value
 
     def GetDefaultItems(self):
+        "Return dictionary of default configuration settings."
         d_items={'main':{}, 'highlight':{}, 'keys':{}, 'extensions':{}}
         for config_type in d_items:
             sections = idleConf.GetSectionList('default', config_type)
@@ -646,6 +729,7 @@
         return d_items
 
     def set_theme_type(self):
+        "Set available screen options based on builtin or custom theme."
         if self.is_builtin_theme.get():
             self.opt_menu_theme_builtin.config(state=NORMAL)
             self.opt_menu_theme_custom.config(state=DISABLED)
@@ -657,6 +741,7 @@
             self.button_delete_custom_theme.config(state=NORMAL)
 
     def set_keys_type(self):
+        "Set available screen options based on builtin or custom key set."
         if self.are_keys_builtin.get():
             self.opt_menu_keys_builtin.config(state=NORMAL)
             self.opt_menu_keys_custom.config(state=DISABLED)
@@ -668,31 +753,39 @@
             self.button_delete_custom_keys.config(state=NORMAL)
 
     def get_new_keys(self):
+        """Handle event to change key binding for selected line.
+
+        A selection of a key/binding in the list of current
+        bindings pops up a dialog to enter a new binding.  If
+        the current key set is builtin and a binding has
+        changed, then a name for a custom key set needs to be
+        entered for the change to be applied.
+        """
         list_index = self.list_bindings.index(ANCHOR)
         binding = self.list_bindings.get(list_index)
-        bind_name = binding.split()[0] #first part, up to first space
+        bind_name = binding.split()[0]
         if self.are_keys_builtin.get():
             current_key_set_name = self.builtin_keys.get()
         else:
             current_key_set_name = self.custom_keys.get()
         current_bindings = idleConf.GetCurrentKeySet()
-        if current_key_set_name in self.changed_items['keys']: #unsaved changes
+        if current_key_set_name in self.changed_items['keys']:  # unsaved changes
             key_set_changes = self.changed_items['keys'][current_key_set_name]
             for event in key_set_changes:
                 current_bindings[event] = key_set_changes[event].split()
         current_key_sequences = list(current_bindings.values())
         new_keys = GetKeysDialog(self, 'Get New Keys', bind_name,
                 current_key_sequences).result
-        if new_keys: #new keys were specified
-            if self.are_keys_builtin.get(): #current key set is a built-in
+        if new_keys:
+            if self.are_keys_builtin.get():  # Current key set is a built-in.
                 message = ('Your changes will be saved as a new Custom Key Set.'
                            ' Enter a name for your new Custom Key Set below.')
                 new_keyset = self.get_new_keys_name(message)
-                if not new_keyset: #user cancelled custom key set creation
+                if not new_keyset:  # User cancelled custom key set creation.
                     self.list_bindings.select_set(list_index)
                     self.list_bindings.select_anchor(list_index)
                     return
-                else: #create new custom key set based on previously active key set
+                else:  # Create new custom key set based on previously active key set.
                     self.create_new_key_set(new_keyset)
             self.list_bindings.delete(list_index)
             self.list_bindings.insert(list_index, bind_name+' - '+new_keys)
@@ -704,6 +797,7 @@
             self.list_bindings.select_anchor(list_index)
 
     def get_new_keys_name(self, message):
+        "Return new key set name from query popup."
         used_names = (idleConf.GetSectionList('user', 'keys') +
                 idleConf.GetSectionList('default', 'keys'))
         new_keyset = SectionName(
@@ -711,34 +805,40 @@
         return new_keyset
 
     def save_as_new_key_set(self):
+        "Prompt for name of new key set and save changes using that name."
         new_keys_name = self.get_new_keys_name('New Key Set Name:')
         if new_keys_name:
             self.create_new_key_set(new_keys_name)
 
     def keybinding_selected(self, event):
+        "Activate button to assign new keys to selected action."
         self.button_new_keys.config(state=NORMAL)
 
     def create_new_key_set(self, new_key_set_name):
-        #creates new custom key set based on the previously active key set,
-        #and makes the new key set active
+        """Create a new custom key set with the given name.
+
+        Create the new key set based on the previously active set
+        with the current changes applied.  Once it is saved, then
+        activate the new key set.
+        """
         if self.are_keys_builtin.get():
             prev_key_set_name = self.builtin_keys.get()
         else:
             prev_key_set_name = self.custom_keys.get()
         prev_keys = idleConf.GetCoreKeys(prev_key_set_name)
         new_keys = {}
-        for event in prev_keys: #add key set to changed items
-            event_name = event[2:-2] #trim off the angle brackets
+        for event in prev_keys:  # Add key set to changed items.
+            event_name = event[2:-2]  # Trim off the angle brackets.
             binding = ' '.join(prev_keys[event])
             new_keys[event_name] = binding
-        #handle any unsaved changes to prev key set
+        # Handle any unsaved changes to prev key set.
         if prev_key_set_name in self.changed_items['keys']:
             key_set_changes = self.changed_items['keys'][prev_key_set_name]
             for event in key_set_changes:
                 new_keys[event] = key_set_changes[event]
-        #save the new theme
+        # Save the new key set.
         self.save_new_key_set(new_key_set_name, new_keys)
-        #change gui over to the new key set
+        # Change GUI over to the new key set.
         custom_key_list = idleConf.GetSectionList('user', 'keys')
         custom_key_list.sort()
         self.opt_menu_keys_custom.SetMenu(custom_key_list, new_key_set_name)
@@ -746,7 +846,12 @@
         self.set_keys_type()
 
     def load_keys_list(self, keyset_name):
+        """Reload the list of action/key binding pairs for the active key set.
+
+        An action/key binding can be selected to change the key binding.
+        """
         reselect = 0
+        # XXX - new_keyset isn't used in this function.
         new_keyset = 0
         if self.list_bindings.curselection():
             reselect = 1
@@ -756,10 +861,10 @@
         bind_names.sort()
         self.list_bindings.delete(0, END)
         for bind_name in bind_names:
-            key = ' '.join(keyset[bind_name]) #make key(s) into a string
-            bind_name = bind_name[2:-2] #trim off the angle brackets
+            key = ' '.join(keyset[bind_name])
+            bind_name = bind_name[2:-2]  # Trim off the angle brackets.
             if keyset_name in self.changed_items['keys']:
-                #handle any unsaved changes to this key set
+                # Handle any unsaved changes to this key set.
                 if bind_name in self.changed_items['keys'][keyset_name]:
                     key = self.changed_items['keys'][keyset_name][bind_name]
             self.list_bindings.insert(END, bind_name+' - '+key)
@@ -769,19 +874,25 @@
             self.list_bindings.select_anchor(list_index)
 
     def delete_custom_keys(self):
+        """Handle event to delete a custom key set.
+
+        Applying the delete deactivates the current configuration and
+        reverts to the default.  The custom key set is permanently
+        deleted from the config file.
+        """
         keyset_name=self.custom_keys.get()
         delmsg = 'Are you sure you wish to delete the key set %r ?'
         if not tkMessageBox.askyesno(
                 'Delete Key Set',  delmsg % keyset_name, parent=self):
             return
         self.deactivate_current_config()
-        #remove key set from config
+        # Remove key set from config.
         idleConf.userCfg['keys'].remove_section(keyset_name)
         if keyset_name in self.changed_items['keys']:
             del(self.changed_items['keys'][keyset_name])
-        #write changes
+        # Write changes.
         idleConf.userCfg['keys'].Save()
-        #reload user key set list
+        # Reload user key set list.
         item_list = idleConf.GetSectionList('user', 'keys')
         item_list.sort()
         if not item_list:
@@ -789,30 +900,36 @@
             self.opt_menu_keys_custom.SetMenu(item_list, '- no custom keys -')
         else:
             self.opt_menu_keys_custom.SetMenu(item_list, item_list[0])
-        #revert to default key set
+        # Revert to default key set.
         self.are_keys_builtin.set(idleConf.defaultCfg['main']
                                 .Get('Keys', 'default'))
         self.builtin_keys.set(idleConf.defaultCfg['main'].Get('Keys', 'name')
                              or idleConf.default_keys())
-        #user can't back out of these changes, they must be applied now
+        # User can't back out of these changes, they must be applied now.
         self.save_all_changed_configs()
         self.activate_config_changes()
         self.set_keys_type()
 
     def delete_custom_theme(self):
+        """Handle event to delete custom theme.
+
+        The current theme is deactivated and the default theme is
+        activated.  The custom theme is permanently removed from
+        the config file.
+        """
         theme_name = self.custom_theme.get()
         delmsg = 'Are you sure you wish to delete the theme %r ?'
         if not tkMessageBox.askyesno(
                 'Delete Theme',  delmsg % theme_name, parent=self):
             return
         self.deactivate_current_config()
-        #remove theme from config
+        # Remove theme from config.
         idleConf.userCfg['highlight'].remove_section(theme_name)
         if theme_name in self.changed_items['highlight']:
             del(self.changed_items['highlight'][theme_name])
-        #write changes
+        # Write changes.
         idleConf.userCfg['highlight'].Save()
-        #reload user theme list
+        # Reload user theme list.
         item_list = idleConf.GetSectionList('user', 'highlight')
         item_list.sort()
         if not item_list:
@@ -820,37 +937,43 @@
             self.opt_menu_theme_custom.SetMenu(item_list, '- no custom themes -')
         else:
             self.opt_menu_theme_custom.SetMenu(item_list, item_list[0])
-        #revert to default theme
+        # Revert to default theme.
         self.is_builtin_theme.set(idleConf.defaultCfg['main'].Get('Theme', 'default'))
         self.builtin_theme.set(idleConf.defaultCfg['main'].Get('Theme', 'name'))
-        #user can't back out of these changes, they must be applied now
+        # User can't back out of these changes, they must be applied now.
         self.save_all_changed_configs()
         self.activate_config_changes()
         self.set_theme_type()
 
     def get_colour(self):
+        """Handle button to select a new color for the target tag.
+
+        If a new color is selected while using a builtin theme, a
+        name must be supplied to create a custom theme.
+        """
         target = self.highlight_target.get()
         prev_colour = self.frame_colour_set.cget('bg')
         rgbTuplet, colour_string = tkColorChooser.askcolor(
                 parent=self, title='Pick new colour for : '+target,
                 initialcolor=prev_colour)
         if colour_string and (colour_string != prev_colour):
-            #user didn't cancel, and they chose a new colour
-            if self.is_builtin_theme.get():  #current theme is a built-in
+            # User didn't cancel and they chose a new colour.
+            if self.is_builtin_theme.get():  # Current theme is a built-in.
                 message = ('Your changes will be saved as a new Custom Theme. '
                            'Enter a name for your new Custom Theme below.')
                 new_theme = self.get_new_theme_name(message)
-                if not new_theme:  #user cancelled custom theme creation
+                if not new_theme:  # User cancelled custom theme creation.
                     return
-                else:  #create new custom theme based on previously active theme
+                else:  # Create new custom theme based on previously active theme.
                     self.create_new_theme(new_theme)
                     self.colour.set(colour_string)
-            else:  #current theme is user defined
+            else:  # Current theme is user defined.
                 self.colour.set(colour_string)
 
     def on_new_colour_set(self):
+        "Display sample of new color selection on the dialog."
         new_colour=self.colour.get()
-        self.frame_colour_set.config(bg=new_colour)  #set sample
+        self.frame_colour_set.config(bg=new_colour)  # Set sample.
         plane ='foreground' if self.fg_bg_toggle.get() else 'background'
         sample_element = self.theme_elements[self.highlight_target.get()][0]
         self.text_highlight_sample.tag_config(sample_element, **{plane:new_colour})
@@ -859,6 +982,7 @@
         self.add_changed_item('highlight', theme, theme_element, new_colour)
 
     def get_new_theme_name(self, message):
+        "Return name of new theme from query popup."
         used_names = (idleConf.GetSectionList('user', 'highlight') +
                 idleConf.GetSectionList('default', 'highlight'))
         new_theme = SectionName(
@@ -866,13 +990,18 @@
         return new_theme
 
     def save_as_new_theme(self):
+        "Prompt for new theme name and create the theme."
         new_theme_name = self.get_new_theme_name('New Theme Name:')
         if new_theme_name:
             self.create_new_theme(new_theme_name)
 
     def create_new_theme(self, new_theme_name):
-        #creates new custom theme based on the previously active theme,
-        #and makes the new theme active
+        """Create a new custom theme with the given name.
+
+        Create the new theme based on the previously active theme
+        with the current changes applied.  Once it is saved, then
+        activate the new theme.
+        """
         if self.is_builtin_theme.get():
             theme_type = 'default'
             theme_name = self.builtin_theme.get()
@@ -880,14 +1009,14 @@
             theme_type = 'user'
             theme_name = self.custom_theme.get()
         new_theme = idleConf.GetThemeDict(theme_type, theme_name)
-        #apply any of the old theme's unsaved changes to the new theme
+        # Apply any of the old theme's unsaved changes to the new theme.
         if theme_name in self.changed_items['highlight']:
             theme_changes = self.changed_items['highlight'][theme_name]
             for element in theme_changes:
                 new_theme[element] = theme_changes[element]
-        #save the new theme
+        # Save the new theme.
         self.save_new_theme(new_theme_name, new_theme)
-        #change gui over to the new theme
+        # Change GUI over to the new theme.
         custom_theme_list = idleConf.GetSectionList('user', 'highlight')
         custom_theme_list.sort()
         self.opt_menu_theme_custom.SetMenu(custom_theme_list, new_theme_name)
@@ -895,11 +1024,17 @@
         self.set_theme_type()
 
     def on_list_fonts_button_release(self, event):
+        """Handle event of selecting a font from the list.
+
+        Change the font name to the font selected from the list
+        and update sample text to show that font.
+        """
         font = self.list_fonts.get(ANCHOR)
         self.font_name.set(font.lower())
         self.set_font_sample()
 
     def set_font_sample(self, event=None):
+        "Update the screen samples with the font settings from the dialog."
         font_name = self.font_name.get()
         font_weight = tkFont.BOLD if self.font_bold.get() else tkFont.NORMAL
         new_font = (font_name, self.font_size.get(), font_weight)
@@ -907,38 +1042,42 @@
         self.text_highlight_sample.configure(font=new_font)
 
     def set_highlight_target(self):
-        if self.highlight_target.get() == 'Cursor':  #bg not possible
+        "Set fg/bg toggle and color based on highlight tag target."
+        if self.highlight_target.get() == 'Cursor':  # bg not possible
             self.radio_fg.config(state=DISABLED)
             self.radio_bg.config(state=DISABLED)
             self.fg_bg_toggle.set(1)
-        else:  #both fg and bg can be set
+        else:  # Both fg and bg can be set.
             self.radio_fg.config(state=NORMAL)
             self.radio_bg.config(state=NORMAL)
             self.fg_bg_toggle.set(1)
         self.set_colour_sample()
 
     def set_colour_sample_binding(self, *args):
+        "Change color sample based on foreground/background toggle."
         self.set_colour_sample()
 
     def set_colour_sample(self):
-        #set the colour smaple area
+        "Set the color of the frame background to reflect the selected target."
+        # Set the colour sample area.
         tag = self.theme_elements[self.highlight_target.get()][0]
         plane = 'foreground' if self.fg_bg_toggle.get() else 'background'
         colour = self.text_highlight_sample.tag_cget(tag, plane)
         self.frame_colour_set.config(bg=colour)
 
     def paint_theme_sample(self):
-        if self.is_builtin_theme.get():  #a default theme
+        "Apply the theme colors to each element tag in the sample text."
+        if self.is_builtin_theme.get():  # Default theme
             theme = self.builtin_theme.get()
-        else:  #a user theme
+        else:  # User theme
             theme = self.custom_theme.get()
         for element_title in self.theme_elements:
             element = self.theme_elements[element_title][0]
             colours = idleConf.GetHighlight(theme, element)
-            if element == 'cursor': #cursor sample needs special painting
+            if element == 'cursor':  # Cursor sample needs special painting.
                 colours['background'] = idleConf.GetHighlight(
                         theme, 'normal', fgBg='bg')
-            #handle any unsaved changes to this theme
+            # Handle any unsaved changes to this theme.
             if theme in self.changed_items['highlight']:
                 theme_dict = self.changed_items['highlight'][theme]
                 if element + '-foreground' in theme_dict:
@@ -949,21 +1088,28 @@
         self.set_colour_sample()
 
     def help_source_selected(self, event):
+        "Handle event for selecting additional help."
         self.set_helplist_button_states()
 
     def set_helplist_button_states(self):
-        if self.list_help.size() < 1:  #no entries in list
+        "Toggle the state for the help list buttons based on list entries."
+        if self.list_help.size() < 1:  # No entries in list.
             self.button_helplist_edit.config(state=DISABLED)
             self.button_helplist_remove.config(state=DISABLED)
-        else: #there are some entries
-            if self.list_help.curselection():  #there currently is a selection
+        else:  # Some entries.
+            if self.list_help.curselection():  # There currently is a selection.
                 self.button_helplist_edit.config(state=NORMAL)
                 self.button_helplist_remove.config(state=NORMAL)
-            else:  #there currently is not a selection
+            else:  # There currently is not a selection.
                 self.button_helplist_edit.config(state=DISABLED)
                 self.button_helplist_remove.config(state=DISABLED)
 
     def helplist_item_add(self):
+        """Handle add button for the help list.
+
+        Query for name and location of new help sources and add
+        them to the list.
+        """
         help_source = HelpSource(self, 'New Help Source',
                                 ).result
         if help_source:
@@ -973,6 +1119,11 @@
         self.set_helplist_button_states()
 
     def helplist_item_edit(self):
+        """Handle edit button for the help list.
+
+        Query with existing help source information and update
+        config if the values are changed.
+        """
         item_index = self.list_help.index(ANCHOR)
         help_source = self.user_helplist[item_index]
         new_help_source = HelpSource(
@@ -988,6 +1139,10 @@
             self.set_helplist_button_states()
 
     def helplist_item_remove(self):
+        """Handle remove button for the help list.
+
+        Delete the help list item from config.
+        """
         item_index = self.list_help.index(ANCHOR)
         del(self.user_helplist[item_index])
         self.list_help.delete(item_index)
@@ -1003,7 +1158,8 @@
                     ';'.join(self.user_helplist[num-1][:2]))
 
     def load_font_cfg(self):
-        ##base editor font selection list
+        "Load current configuration settings for the font options."
+        # Set base editor font selection list.
         fonts = list(tkFont.families(self))
         fonts.sort()
         for font in fonts:
@@ -1021,29 +1177,31 @@
             self.list_fonts.select_anchor(current_font_index)
         except ValueError:
             pass
-        ##font size dropdown
+        # Set font size dropdown.
         self.opt_menu_font_size.SetMenu(('7', '8', '9', '10', '11', '12', '13',
                                       '14', '16', '18', '20', '22',
                                       '25', '29', '34', '40'), font_size )
-        ##font_weight
+        # Set font weight.
         self.font_bold.set(font_bold)
-        ##font sample
+        # Set font sample.
         self.set_font_sample()
 
     def load_tab_cfg(self):
-        ##indent sizes
+        "Load current configuration settings for the tab options."
+        # Set indent sizes.
         space_num = idleConf.GetOption(
             'main', 'Indent', 'num-spaces', default=4, type='int')
         self.space_num.set(space_num)
 
     def load_theme_cfg(self):
-        ##current theme type radiobutton
+        "Load current configuration settings for the theme options."
+        # Set current theme type radiobutton.
         self.is_builtin_theme.set(idleConf.GetOption(
                 'main', 'Theme', 'default', type='bool', default=1))
-        ##currently set theme
+        # Set current theme.
         current_option = idleConf.CurrentTheme()
-        ##load available theme option menus
-        if self.is_builtin_theme.get(): #default theme selected
+        # Load available theme option menus.
+        if self.is_builtin_theme.get():  # Default theme selected.
             item_list = idleConf.GetSectionList('default', 'highlight')
             item_list.sort()
             self.opt_menu_theme_builtin.SetMenu(item_list, current_option)
@@ -1054,7 +1212,7 @@
                 self.custom_theme.set('- no custom themes -')
             else:
                 self.opt_menu_theme_custom.SetMenu(item_list, item_list[0])
-        else: #user theme selected
+        else:  # User theme selected.
             item_list = idleConf.GetSectionList('user', 'highlight')
             item_list.sort()
             self.opt_menu_theme_custom.SetMenu(item_list, current_option)
@@ -1062,7 +1220,7 @@
             item_list.sort()
             self.opt_menu_theme_builtin.SetMenu(item_list, item_list[0])
         self.set_theme_type()
-        ##load theme element option menu
+        # Load theme element option menu.
         theme_names = list(self.theme_elements.keys())
         theme_names.sort(key=lambda x: self.theme_elements[x][1])
         self.opt_menu_highlight_target.SetMenu(theme_names, theme_names[0])
@@ -1070,13 +1228,14 @@
         self.set_highlight_target()
 
     def load_key_cfg(self):
-        ##current keys type radiobutton
+        "Load current configuration settings for the keybinding options."
+        # Set current keys type radiobutton.
         self.are_keys_builtin.set(idleConf.GetOption(
                 'main', 'Keys', 'default', type='bool', default=1))
-        ##currently set keys
+        # Set current keys.
         current_option = idleConf.CurrentKeys()
-        ##load available keyset option menus
-        if self.are_keys_builtin.get(): #default theme selected
+        # Load available keyset option menus.
+        if self.are_keys_builtin.get():  # Default theme selected.
             item_list = idleConf.GetSectionList('default', 'keys')
             item_list.sort()
             self.opt_menu_keys_builtin.SetMenu(item_list, current_option)
@@ -1087,7 +1246,7 @@
                 self.custom_keys.set('- no custom keys -')
             else:
                 self.opt_menu_keys_custom.SetMenu(item_list, item_list[0])
-        else: #user key set selected
+        else:  # User key set selected.
             item_list = idleConf.GetSectionList('user', 'keys')
             item_list.sort()
             self.opt_menu_keys_custom.SetMenu(item_list, current_option)
@@ -1095,50 +1254,48 @@
             item_list.sort()
             self.opt_menu_keys_builtin.SetMenu(item_list, idleConf.default_keys())
         self.set_keys_type()
-        ##load keyset element list
+        # Load keyset element list.
         keyset_name = idleConf.CurrentKeys()
         self.load_keys_list(keyset_name)
 
     def load_general_cfg(self):
-        #startup state
+        "Load current configuration settings for the general options."
+        # Set startup state.
         self.startup_edit.set(idleConf.GetOption(
                 'main', 'General', 'editor-on-startup', default=1, type='bool'))
-        #autosave state
+        # Set autosave state.
         self.autosave.set(idleConf.GetOption(
                 'main', 'General', 'autosave', default=0, type='bool'))
-        #initial window size
+        # Set initial window size.
         self.win_width.set(idleConf.GetOption(
                 'main', 'EditorWindow', 'width', type='int'))
         self.win_height.set(idleConf.GetOption(
                 'main', 'EditorWindow', 'height', type='int'))
-        # default source encoding
+        # Set default source encoding.
         self.encoding.set(idleConf.GetOption(
                 'main', 'EditorWindow', 'encoding', default='none'))
-        # additional help sources
+        # Set additional help sources.
         self.user_helplist = idleConf.GetAllExtraHelpSourcesList()
         for help_item in self.user_helplist:
             self.list_help.insert(END, help_item[0])
         self.set_helplist_button_states()
 
     def load_configs(self):
-        """
-        load configuration from default and user config files and populate
+        """Load configuration for each page.
+
+        Load configuration from default and user config files and populate
         the widgets on the config dialog pages.
         """
-        ### fonts / tabs page
         self.load_font_cfg()
         self.load_tab_cfg()
-        ### highlighting page
         self.load_theme_cfg()
-        ### keys page
         self.load_key_cfg()
-        ### general page
         self.load_general_cfg()
         # note: extension page handled separately
 
     def save_new_key_set(self, keyset_name, keyset):
-        """
-        save a newly created core key set.
+        """Save a newly created core key set.
+
         keyset_name - string, the name of the new key set
         keyset - dictionary containing the new key set
         """
@@ -1149,8 +1306,8 @@
             idleConf.userCfg['keys'].SetOption(keyset_name, event, value)
 
     def save_new_theme(self, theme_name, theme):
-        """
-        save a newly created theme.
+        """Save a newly created theme.
+
         theme_name - string, the name of the new theme
         theme - dictionary containing the new theme
         """
@@ -1161,21 +1318,22 @@
             idleConf.userCfg['highlight'].SetOption(theme_name, element, value)
 
     def set_user_value(self, config_type, section, item, value):
+        "Return True if the configuration value was added or changed."
         if idleConf.defaultCfg[config_type].has_option(section, item):
             if idleConf.defaultCfg[config_type].Get(section, item) == value:
-                #the setting equals a default setting, remove it from user cfg
+                # The setting equals a default setting, remove it from user cfg.
                 return idleConf.userCfg[config_type].RemoveOption(section, item)
-        #if we got here set the option
+        # If we got here, set the option.
         return idleConf.userCfg[config_type].SetOption(section, item, value)
 
     def save_all_changed_configs(self):
-        "Save configuration changes to the user config file."
+        "Save all configuration changes to the user config file."
         idleConf.userCfg['main'].Save()
         for config_type in self.changed_items:
             cfg_type_changed = False
             for section in self.changed_items[config_type]:
                 if section == 'HelpFiles':
-                    #this section gets completely replaced
+                    # This section gets completely replaced.
                     idleConf.userCfg['main'].remove_section('HelpFiles')
                     cfg_type_changed = True
                 for item in self.changed_items[config_type][section]:
@@ -1185,14 +1343,15 @@
             if cfg_type_changed:
                 idleConf.userCfg[config_type].Save()
         for config_type in ['keys', 'highlight']:
-            # save these even if unchanged!
+            # Save these even if unchanged!
             idleConf.userCfg[config_type].Save()
-        self.reset_changed_items() #clear the changed items dict
-        self.save_all_changed_extensions()  # uses a different mechanism
+        self.reset_changed_items()  # Clear the changed items dict.
+        self.save_all_changed_extensions()  # Uses a different mechanism.
 
     def deactivate_current_config(self):
-        #Before a config is saved, some cleanup of current
-        #config must be done - remove the previous keybindings
+        "Remove current key bindings."
+        # Before a config is saved, some cleanup of current
+        # config must be done - remove the previous keybindings.
         win_instances = self.parent.instance_dict.keys()
         for instance in win_instances:
             instance.RemoveKeybindings()
@@ -1208,18 +1367,22 @@
             instance.reset_help_menu_entries()
 
     def cancel(self):
+        "Dismiss config dialog."
         self.destroy()
 
     def ok(self):
+        "Apply config changes, then dismiss dialog."
         self.apply()
         self.destroy()
 
     def apply(self):
+        "Apply config changes and leave dialog open."
         self.deactivate_current_config()
         self.save_all_changed_configs()
         self.activate_config_changes()
 
     def help(self):
+        "Create textview for config dialog help."
         page = self.tab_pages._current_page
         view_text(self, title='Help for IDLE preferences',
                  text=help_common+help_pages.get(page, ''))
@@ -1247,8 +1410,8 @@
         self.ext_userCfg = idleConf.userCfg['extensions']
         self.is_int = self.register(is_int)
         self.load_extensions()
-        # create widgets - a listbox shows all available extensions, with the
-        # controls for the extension selected in the listbox to the right
+        # Create widgets - a listbox shows all available extensions, with the
+        # controls for the extension selected in the listbox to the right.
         self.extension_names = StringVar(self)
         frame.rowconfigure(0, weight=1)
         frame.columnconfigure(2, weight=1)
@@ -1268,7 +1431,7 @@
         self.outerframe = self                      # TEMPORARY
         self.tabbed_page_set = self.extension_list  # TEMPORARY
 
-        # create the frame holding controls for each extension
+        # Create the frame holding controls for each extension.
         ext_names = ''
         for ext_name in sorted(self.extensions):
             self.create_extension_frame(ext_name)
@@ -1286,7 +1449,7 @@
         for ext_name in self.extensions:
             opt_list = sorted(self.ext_defaultCfg.GetOptionList(ext_name))
 
-            # bring 'enable' options to the beginning of the list
+            # Bring 'enable' options to the beginning of the list.
             enables = [opt_name for opt_name in opt_list
                        if opt_name.startswith('enable')]
             for opt_name in enables:
@@ -1310,8 +1473,8 @@
                     value = self.ext_userCfg.Get(
                             ext_name, opt_name, type=opt_type, raw=True,
                             default=def_obj)
-                except ValueError:  # Need this until .Get fixed
-                    value = def_obj  # bad values overwritten by entry
+                except ValueError:  # Need this until .Get fixed.
+                    value = def_obj  # Bad values overwritten by entry.
                 var = StringVar(self)
                 var.set(str(value))
 
@@ -1323,6 +1486,7 @@
                                                  })
 
     def extension_selected(self, event):
+        "Handle selection of an extension from the list."
         newsel = self.extension_list.curselection()
         if newsel:
             newsel = self.extension_list.get(newsel)
@@ -1341,9 +1505,9 @@
         f = VerticalScrolledFrame(self.details_frame, height=250, width=250)
         self.config_frame[ext_name] = f
         entry_area = f.interior
-        # create an entry for each configuration option
+        # Create an entry for each configuration option.
         for row, opt in enumerate(self.extensions[ext_name]):
-            # create a row with a label and entry/checkbutton
+            # Create a row with a label and entry/checkbutton.
             label = Label(entry_area, text=opt['name'])
             label.grid(row=row, column=0, sticky=NW)
             var = opt['var']
@@ -1363,15 +1527,20 @@
         return
 
     def set_extension_value(self, section, opt):
+        """Return True if the configuration was added or changed.
+
+        If the value is the same as the default, then remove it
+        from user config file.
+        """
         name = opt['name']
         default = opt['default']
         value = opt['var'].get().strip() or default
         opt['var'].set(value)
         # if self.defaultCfg.has_section(section):
-        # Currently, always true; if not, indent to return
+        # Currently, always true; if not, indent to return.
         if (value == default):
             return self.ext_userCfg.RemoveOption(section, name)
-        # set the option
+        # Set the option.
         return self.ext_userCfg.SetOption(section, name, value)
 
     def save_all_changed_extensions(self):
@@ -1446,7 +1615,7 @@
     def __init__(self, parent, *args, **kw):
         Frame.__init__(self, parent, *args, **kw)
 
-        # create a canvas object and a vertical scrollbar for scrolling it
+        # Create a canvas object and a vertical scrollbar for scrolling it.
         vscrollbar = Scrollbar(self, orient=VERTICAL)
         vscrollbar.pack(fill=Y, side=RIGHT, expand=FALSE)
         canvas = Canvas(self, bd=0, highlightthickness=0,
@@ -1454,25 +1623,25 @@
         canvas.pack(side=LEFT, fill=BOTH, expand=TRUE)
         vscrollbar.config(command=canvas.yview)
 
-        # reset the view
+        # Reset the view.
         canvas.xview_moveto(0)
         canvas.yview_moveto(0)
 
-        # create a frame inside the canvas which will be scrolled with it
+        # Create a frame inside the canvas which will be scrolled with it.
         self.interior = interior = Frame(canvas)
         interior_id = canvas.create_window(0, 0, window=interior, anchor=NW)
 
-        # track changes to the canvas and frame width and sync them,
-        # also updating the scrollbar
+        # Track changes to the canvas and frame width and sync them,
+        # also updating the scrollbar.
         def _configure_interior(event):
-            # update the scrollbars to match the size of the inner frame
+            # Update the scrollbars to match the size of the inner frame.
             size = (interior.winfo_reqwidth(), interior.winfo_reqheight())
             canvas.config(scrollregion="0 0 %s %s" % size)
         interior.bind('<Configure>', _configure_interior)
 
         def _configure_canvas(event):
             if interior.winfo_reqwidth() != canvas.winfo_width():
-                # update the inner frame's width to fill the canvas
+                # Update the inner frame's width to fill the canvas.
                 canvas.itemconfigure(interior_id, width=canvas.winfo_width())
         canvas.bind('<Configure>', _configure_canvas)