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Switchboard class. This class is used to coordinate updates among all Viewers. Every Viewer must conform to the following interface: - it must include a method called update_yourself() which takes three arguments; the red, green, and blue values of the selected color. - When a Viewer selects a color and wishes to update all other Views, it should call update_views() on the Switchboard object. Note that the Viewer typically does *not* update itself before calling update_views(), since this would cause it to get updated twice. Optionally, Viewers can also implement: - save_options() which takes an optiondb (a dictionary). Store into this dictionary any values the Viewer wants to save in the persistent ~/.pynche file. This dictionary is saved using marshal. The namespace for the keys is ad-hoc; make sure you don't clobber some other Viewer's keys! - withdraw() which takes no arguments. This is called when Pynche is unmapped. All Viewers should implement this. - colordb_changed() which takes a single argument, an instance of ColorDB. This is called whenever the color name database is changed and gives a chance for the Viewers to do something on those events. See ListViewer for details. External Viewers are found dynamically. Viewer modules should have names such as FooViewer.py. If such a named module has a module global variable called ADDTOVIEW and this variable is true, the Viewer will be added dynamically to the `View' menu. ADDTOVIEW contains a string which is used as the menu item to display the Viewer (one kludge: if the string contains a `%', this is used to indicate that the next character will get an underline in the menu, otherwise the first character is underlined). FooViewer.py should contain a class called FooViewer, and its constructor should take two arguments, an instance of Switchboard, and optionally a Tk master window.