Module Structure

PAGE generates two modules, The GUI module, and the Support Module. The first contains all of the Python code necessary to plop the GUI window onto the computer screen. In my vision of the PAGE word, the GUI module is not to be edited. It contains all of the required linkage to the Support module. It is generally the main module of the application.

The Support module is generated in skeletal form and is the framework upon which the application is built. It is where the user written code resides. As such it is infrequently generated or replaced by PAGE. In fact, the separation is the secret of rework; it allows changes to the content and appearance of the GUI window while preserving the user’s code.

GUI Module

The main feature of the GUI module is the class definition, which defines a GUI window. It defines the top level window and all of the contained widgets. Note that it refers to all callback functions as functions in the support module and that Tk variables such as textvariables are referred to Tk variables in the support module.

The GUI module contains two stylized function for instantiating the window class. They are:

def vp_start_gui():
        '''Starting point when module is the main routine.'''
    global val, w, root
    root = Tk()
    top = New_Toplevel_1 (root)
    fnew_support.init(root, top)
    root.mainloop()

which is the entry point when starting the routine as the main routine of the application as seen at the bottom of the module:

if __name__ == '__main__':
   vp_start_gui()

The main thing about the function vp_start_gui is that it initializes Tk and establishes the Tkinter mainloop. Note that the init function in the support module is passed pointer to the GUI window class.

and

def create_New_Toplevel_1(root, *args, **kwargs):
    '''Starting point when module is imported by another
    program.'''
    global w, w_win, rt
    rt = root
    w = Toplevel (root)
    top = New_Toplevel_1 (w)
    fnew_support.init(w, top, *args, **kwargs)
    return (w, top)

which is the entry point when ate GUI window is invoked from code within the running application. For instance, A secondary GUI such as a progress bar is desired for some action triggered in the main GUI. Notice that it does not call Tk() nor start a mainloop; you only want one of those. A big point is that the init function is passed a variable argument list in the name of flexibility. It is also passed a pointer to the GUI window. This is done so that the user can close the created window in its support module without closing affecting other windows in the application.

Support Module

This module is home of the hand coded portion of the application. Obviously, PAGE can only prepare a framework for the application. What PAGE knows about are, (1) the linkage between the GUI module and the support module, (2) the callback functions to be located in the Support module, and (3) the Tk variables which are to be manipulated in the support module.

For linkage between the modules is mainly the init function.

def init(top, gui, *args, **kwargs):
        global w, top_level, root
    w = gui
    top_level = top
    root = top

Here PAGE merely generates the bare minimum. It sets global variables which refer to the root of the GUI window “root = top” and w which points to the GUI window. The latter allow the user to change configuration of the GUI window and of widget contained in the window. For instance if there is a button (Button1) in the GUI window, the color may be changed anywhere in the support module simply with the following code:

w.Button1.configure(color='red')

Also, if there is hierarchy of modules or routines flowing from the support module, then the reference to the GUI window can be passed along and manipulated.

The generated code for the callback functions is even simpler:

def callback():
    print('unknown_support.callback')
    sys.stdout.flush()

Code generated for the Tk variable kkkk looks like:

def set_Tk_var():
   # These are Tk variables used passed to Tkinter and must be
   # defined before the widgets using them are created.
   global kkkk
   kkkk = StringVar()

The code generated as above is so generated so that the GUI module and the support module will be an executable pair. That is, you can execute the GUI module and see what it will look like even though you have put in no additional application code. If the GUI invokes a callback, say by a button select, the program will tell you that it was invoked. Now you have a leg up, go program.

What if after you have written a substantial body of application code, and discover that you need an additional widget in the GUI module; what to do?

First invoke PAGE with the project name, add the widget with all its configuration including callbacks and Tk variables. Then generate Python code for the GUI module just like before. You sure do not want to rebuild the support module anew and erase all of your hand code. So when you tell PAGE to generate your support module, it gives you the option of updating the existing support module. If selected, PAGE will merely add skeletons for the new callbacks and add the new Tk variables. In addition, it will backup the previous version of the modules in case of failure or PAGE bugs. etc.. PAGE will keep backups five deep.

As a convenience, the following code is added at the bottom of the support module to aid in debugging. I you are debugging the support module and want to test its execution, you can just execute it and it will not start by invoking a functions within the support module but rather the main function in the GUI module. I found it particularly useful since I do my development in emacs where I have a key binding which will invoke python to execute the current buffer.

 if __name__ == '__main__':
import bind_example
bind_example.vp_start_gui()

Some of these features are further explored in Applications with Multiple Top-Level Windows.

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