Writing an IDLE extension An IDLE extension can define new key bindings and menu entries for IDLE edit windows. There is a simple mechanism to load extensions when IDLE starts up and to attach them to each edit window. (It is also possible to make other changes to IDLE, but this must be done by editing the IDLE source code.) The list of extensions loaded at startup time is configured by editing the file config.txt; see below for details. An IDLE extension is defined by a class. Methods of the class define actions that are invoked by those bindings or menu entries. Class (or instance) variables define the bindings and menu additions; these are automatically applied by IDLE when the extension is linked to an edit window. An IDLE extension class is instantiated with a single argument, `editwin', an EditorWindow instance. The extension cannot assume much about this argument, but it is guarateed to have the following instance variables: text a Text instance (a widget) io an IOBinding instance (more about this later) flist the FileList instance (shared by all edit windows) (There are a few more, but they are rarely useful.) The extension class must not bind key events. Rather, it must define one or more virtual events, e.g. <>, and corresponding methods, e.g. zoom_height_event(), and have one or more class (or instance) variables that define mappings between virtual events and key sequences, e.g. . When the extension is loaded, these key sequences will be bound to the corresponding virtual events, and the virtual events will be bound to the corresponding methods. (This indirection is done so that the key bindings can easily be changed, and so that other sources of virtual events can exist, such as menu entries.) The following class or instance variables are used to define key bindings for virtual events: keydefs for all platforms mac_keydefs for Macintosh windows_keydefs for Windows unix_keydefs for Unix (and other platforms) Each of these variables, if it exists, must be a dictionary whose keys are virtual events, and whose values are lists of key sequences. An extension can define menu entries in a similar fashion. This is done with a class or instance variable named menudefs; it should be a list of pair, where each pair is a menu name (lowercase) and a list of menu entries. Each menu entry is either None (to insert a separator entry) or a pair of strings (menu_label, virtual_event). Here, menu_label is the label of the menu entry, and virtual_event is the virtual event to be generated when the entry is selected. An underscore in the menu label is removed; the character following the underscore is displayed underlined, to indicate the shortcut character (for Windows). At the moment, extensions cannot define whole new menus; they must define entries in existing menus. Some menus are not present on some windows; such entry definitions are then ignored, but the key bindings are still applied. (This should probably be refined in the future.) Here is a complete example example: class ZoomHeight: menudefs = [ ('edit', [ None, # Separator ('_Zoom Height', '<>'), ]) ] windows_keydefs = { '<>': [''], } unix_keydefs = { '<>': [''], } def __init__(self, editwin): self.editwin = editwin def zoom_height_event(self, event): "...Do what you want here..." The final piece of the puzzle is the file "config.txt", which is used to to configure the loading of extensions. For each extension, you must include a section in config.txt (or in any of the other configuration files that are consulted at startup: config-unix.txt, config-win.txt, or ~/.idle). A section is headed by the module name in square brackets, e.g. [ZoomHeight] The section may be empty, or it may define configuration options for the extension. (See ParenMatch.py for an example.) A special option is 'enable': including enable = 0 in a section disables that extension. More than one configuration file may specify options for the same extension, so a user may disable an extension that is loaded by default, or enable an extension that is disabled by default. Extensions can define key bindings and menu entries that reference events they don't implement (including standard events); however this is not recommended (and may be forbidden in the future). Extensions are not required to define menu entries for all events they implement. Note: in order to change key bindings, you must currently edit the file keydefs. It contains two dictionaries named and formatted like the keydefs dictionaries described above, one for the Unix bindings and one for the Windows bindings. In the future, a better mechanism will be provided.