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author jpayne
date Tue, 18 Mar 2025 16:23:26 -0400
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1 Writing an IDLE extension
2 =========================
3
4 An IDLE extension can define new key bindings and menu entries for IDLE
5 edit windows. There is a simple mechanism to load extensions when IDLE
6 starts up and to attach them to each edit window. (It is also possible
7 to make other changes to IDLE, but this must be done by editing the IDLE
8 source code.)
9
10 The list of extensions loaded at startup time is configured by editing
11 the file config-extensions.def. See below for details.
12
13 An IDLE extension is defined by a class. Methods of the class define
14 actions that are invoked by event bindings or menu entries. Class (or
15 instance) variables define the bindings and menu additions; these are
16 automatically applied by IDLE when the extension is linked to an edit
17 window.
18
19 An IDLE extension class is instantiated with a single argument,
20 `editwin', an EditorWindow instance. The extension cannot assume much
21 about this argument, but it is guaranteed to have the following instance
22 variables:
23
24 text a Text instance (a widget)
25 io an IOBinding instance (more about this later)
26 flist the FileList instance (shared by all edit windows)
27
28 (There are a few more, but they are rarely useful.)
29
30 The extension class must not directly bind Window Manager (e.g. X) events.
31 Rather, it must define one or more virtual events, e.g. <<zoom-height>>, and
32 corresponding methods, e.g. zoom_height_event(). The virtual events will be
33 bound to the corresponding methods, and Window Manager events can then be bound
34 to the virtual events. (This indirection is done so that the key bindings can
35 easily be changed, and so that other sources of virtual events can exist, such
36 as menu entries.)
37
38 An extension can define menu entries. This is done with a class or instance
39 variable named menudefs; it should be a list of pairs, where each pair is a
40 menu name (lowercase) and a list of menu entries. Each menu entry is either
41 None (to insert a separator entry) or a pair of strings (menu_label,
42 virtual_event). Here, menu_label is the label of the menu entry, and
43 virtual_event is the virtual event to be generated when the entry is selected.
44 An underscore in the menu label is removed; the character following the
45 underscore is displayed underlined, to indicate the shortcut character (for
46 Windows).
47
48 At the moment, extensions cannot define whole new menus; they must define
49 entries in existing menus. Some menus are not present on some windows; such
50 entry definitions are then ignored, but key bindings are still applied. (This
51 should probably be refined in the future.)
52
53 Extensions are not required to define menu entries for all the events they
54 implement. (They are also not required to create keybindings, but in that
55 case there must be empty bindings in cofig-extensions.def)
56
57 Here is a complete example:
58
59 class ZoomHeight:
60
61 menudefs = [
62 ('edit', [
63 None, # Separator
64 ('_Zoom Height', '<<zoom-height>>'),
65 ])
66 ]
67
68 def __init__(self, editwin):
69 self.editwin = editwin
70
71 def zoom_height_event(self, event):
72 "...Do what you want here..."
73
74 The final piece of the puzzle is the file "config-extensions.def", which is
75 used to configure the loading of extensions and to establish key (or, more
76 generally, event) bindings to the virtual events defined in the extensions.
77
78 See the comments at the top of config-extensions.def for information. It's
79 currently necessary to manually modify that file to change IDLE's extension
80 loading or extension key bindings.
81
82 For further information on binding refer to the Tkinter Resources web page at
83 python.org and to the Tk Command "bind" man page.