Using python to create Macintosh applications, part two

In this document we rewrite the application of the previous example to use modeless dialogs. We will use an application framework, and we will have a look at creating applets, standalone applications written in Python. The source code and resource file are available in the folder example2.

Again, we start with ResEdit to create our dialogs. Not only do we want a main dialog this time but also an "About" dialog. This example is less than complete since we do not provide a BNDL resource and related stuff that an application cannot be without. We are able to do this when building a python applet since BuildApplet will substitute default resources for BNDL, etc. when none are supplied (See below.) "Inside Mac" or various books on Macintosh programming will help here. Also, you can refer to the resource files provided in the Python source distribution for some of the python-specific points of BNDL programming: the "appletbundle.rsrc" file is what is used for creating applets if you don't provide your own resource file.

When creating your own BNDL resouorces, keep in mind that the Finder gets confused if you have more than one application with the same signature. This may be due to some incorrectness on the side of "BuildApplet", I am not sure. There is one case when you definitely need a unique signature: when you create an applet that has its own data files and you want the user to be able to start your applet by double-clicking one of the datafiles.

Let's have a look at dnslookup-2.rsrc, our resource file. Dialog 512 is the main window which has one button (Lookup), two labels and two text entry areas, one of which is used for output only. The "Quit" and button has disappeared, because its function is handled by a menu choice. Here's what it will look like at run time:

A modeless dialog application using FrameWork

On to the source code in dnslookup-2.py. The start is similar to our previous example program dnslookup-1.py, with one extra module being imported. To make life more simple we will use the FrameWork module, a nifty piece of code that handles all the gory Mac details of event loop programming, menubar installation and all the other code that is the same for every Mac program in the world. Like most standard modules, FrameWork will run some sample test code when you invoke it as a main program, so try it now. It will create a menu bar with an Apple menu with the about box and a "File" menu with some pythonesque choices (which do nothing interesting, by the way) and a "Quit" command that works.

If you have not used FrameWork before you may want to first take a look at the Pathetic EDitor example, which builds a minimal text editor using FrameWork and TextEdit. On the other hand: we don't use many features of FrameWork, so you could also continue with this document.

After the imports we get the definitions of resource-IDs in our resource file, slightly changed from the previous version of our program. The main program is also similar to our previous version, with one important exception: we first check to see whether our resource is available before opening the resource file. Why is this? Because later, when we will have converted the script to an applet, our resources will be available in the applet file and we don't need the separate resource file anymore.

Next comes the definition of our main class, DNSLookup, which inherits FrameWork.Application. The Application class handles the menu bar and the main event loop and event dispatching. In the __init__ routine we first let the base class initialize itself, then we create our modeless dialog and finally we jump into the main loop. The main loop continues until we call self._quit, which we will do when the user selects "Quit". When we create the instance of MyDialog (which inherits DialogWindow, which inherits Window) we pass a reference to the application object, this reference is used to tell Application about our new window. This enables the event loop to keep track of all windows and dispatch things like update events and mouse clicks.

The makeusermenus() method (which is called sometime during the Application __init__ routine) creates a File menu with a Quit command (shortcut command-Q), which will callback to our quit() method. Quit(), in turn, calls _quit which causes the mainloop to terminate at a convenient time.

Application provides a standard about box, but we override this by providing our own do_about() method which shows an about box from a resource as a modal dialog. This piece of code should look familiar to you from the previous example program. That do_about is called when the user selects About from the Apple menu is, again, taken care of by the __init__ routine of Application.

The MyDialog class is the container for our main window. Initialization is again done by first calling the base class __init__ function and finally setting the local variable "parent."

Do_itemhit() is called when an item is selected in this dialog by the user. We are passed the item number (and the original event structure, which we normally ignore). The code is similar to the main loop of our previous example program: a switch depending on the item selected. Dnslookup() is quite similar to our previous example.

Creating applets

Now let us try to turn the python script into an applet, a standalone application. This will not work if you have the "classic 68k" Python distribution, only if you have the cfm68k or PPC distribution.

Actually, "standalone" is probably not the correct term here, since an applet does still depend on a lot of the python environment: the PythonCore shared library, the Python Preferences file, the python Lib folder and any other modules that the main module depends on. It is possible to get rid of all these dependencies and create true standalone applications in Python, but this is a bit difficult. See Standalone Applications in Python for details. For this document, by standalone we mean here that the script has the look-and-feel of an application, including the ability to have its own document types, be droppable, etc.

The easiest way to create an applet is to take your source file and drop it onto "BuildApplet", located in the Python home folder. This will create an applet with the same name as your python source with the ".py" stripped. Also, if a resource file with the same name as your source but with ".rsrc" extension is available the resources from that file will be copied to your applet too. If there is no resource file for your script a set of default resources will be used, and the applet will have the default creator 'Pyt0'. The latter also happens if you do have a resource file but without the BNDL combo. Actually, as in the present example.

If you need slightly more control over the BuildApplet process you can double-click it, and you will get dialogs for source and destination of the applet. The rest of the process, including locating the resource file, remains the same.

Note that though our example application completely bypasses the normal python user interface this is by no means necessary. Any python script can be turned into an applet, and all the usual features of the interpreter still work.

That's all for this example, you may now return to the table of contents to pick another topic.