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9.6 KiB
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<HTML><HEAD><TITLE>Using python to create Macintosh applications, part two</TITLE></HEAD>
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<BODY>
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<H1>Using python to create Macintosh applications, part two</H1>
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<HR>
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In this document we rewrite the application of the <A
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HREF="example1.html">previous example</A> to use modeless dialogs. We
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will use an application framework, and we will have a look at creating
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applets, standalone applications written in Python. <A
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HREF="example2/InterslipControl-2.py">Source</A> and resource file (in
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binary and <A HREF="example2/InterslipControl-2.rsrc.hqx">BinHex</A>
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form for downloading) are available in the folder <A
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HREF="example2">example2</A>. <p>
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Again, we start with ResEdit to create our dialogs. Not only do we
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want a main dialog this time but also an "About" dialog, and we
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provide the <A NAME="bundle">BNDL resource</A> and related stuff that
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an application cannot be without. (Actually, a python applet can be
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without, <A HREF="#no-bundle">see below</A>). "Inside Mac" or various
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books on macintosh programming will help here. Also, you can refer to
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the resource files provided in the Python source distribution for some
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of the python-specific points of BNDL programming: the
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"appletbundle.rsrc" file is what is used for creating applets if you
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don't provide your own resource file. <p>
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Let's have a look at InterslipControl-2.rsrc, our resource file. First
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off, there's the standard BNDL combo. I've picked 'PYTi' as signature
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for the application. I tend to pick PYT plus one lower-case letter for
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my signatures. The finder gets confused if you have two applications
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with the same signature. This may be due to some incorrectness on the
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side of "BuildApplet", I am not sure. There is one case when you
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definitely need a unique signature: when you create an applet that has
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its own data files and you want the user to be able to start your
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applet by double-clicking one of the datafiles. <p>
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There's little to tell about the BNDL stuff: I basically copied the
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generic Python applet icons and pasted in the symbol for
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InterSLIP. The two dialogs are equally unexciting: dialog 512 is our
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main window which has four static text fields (two of which we will be
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modifying during runtime, to show the status of the connection) and
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two buttons "connect" and "disconnect". The "quit" and "update status"
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buttons have disappeared, because they are handled by a menu choice
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and automatically, respectively. <p>
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<H2>A modeless dialog application using FrameWork</H2>
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On to the source code in <A
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HREF="example2/InterslipControl-2.py">InterslipControl-2.py</A>. The
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start is similar to our previous example program <A
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HREF="example1/InterslipControl-1.py">InterSlipControl-1.py</A>, with
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one extra module being imported. To make life more simple we will use
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the <CODE>FrameWork</CODE> module, a nifty piece of code that handles
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all the gory mac details of event loop programming, menubar
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installation and all the other code that is the same for every mac
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program in the world. Like most standard modules, FrameWork will run
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some sample test code when you invoke it as a main program, so try it
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now. It will create a menu bar with an Apple menu with the about box
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and a "File" menu with some pythonesque choices (which do nothing
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interesting, by the way) and a "Quit" command that works. <p>
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<BLOCKQUOTE>
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If you have not used <code>FrameWork</code> before you may want to
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first take a look at the <A HREF="textedit.html">Pathetic EDitor</A>
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example, which builds a minimal text editor using FrameWork and TextEdit.
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On the other hand: we don't use many features of FrameWork, so you could
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also continue with this document.
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</BLOCKQUOTE>
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After the imports we get the definitions of resource-IDs in our
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resource file, slightly changed from the previous version of our
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program, and the state to string mapping. The main program is also
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similar to our previous version, with one important exception: we
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first check to see whether our resource is available before opening
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the resource file. Why is this? Because later, when we will have
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converted the script to an applet, our resources will be available in
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the applet file and we don't need the separate resource file
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anymore. <p>
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Next comes the definition of our main class,
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<CODE>InterslipControl</CODE>, which inherits
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<CODE>FrameWork.Application</CODE>. The Application class handles the
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menu bar and the main event loop and event dispatching. In the
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<CODE>__init__</CODE> routine we first let the base class initialize
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itself, then we create our modeless dialog and finally we jump into
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the main loop. The main loop continues until we call <CODE>self._quit</CODE>,
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which we will do when the user selects "quit". When we create
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the instance of <CODE>MyDialog</CODE> (which inherits
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<CODE>DialogWindow</CODE>, which inherits <CODE>Window</CODE>) we pass
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a reference to the application object, this reference is used to tell
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Application about our new window. This enables the event loop to keep
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track of all windows and dispatch things like update events and mouse
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clicks. <p>
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The <CODE>makeusermenus()</CODE> method (which is called sometime
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during the Application <CODE>__init__</CODE> routine) creates a File
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menu with a Quit command (shortcut command-Q), which will callback to
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our quit() method. <CODE>Quit()</CODE>, in turn, calls <CODE>_quit</CODE> which
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causes the mainloop to terminate at a convenient time. <p>
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Application provides a standard about box, but we override this by
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providing our own <CODE>do_about()</CODE> method which shows an about
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box from a resource as a modal dialog. This piece of code should look
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familiar to you from the previous example program. That do_about is
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called when the user selects About from the Apple menu is, again,
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taken care of by the __init__ routine of Application. <p>
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Our main object finally overrides <CODE>idle()</CODE>, the method
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called when no event is available. It passes the call on to our dialog
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object to give it a chance to update the status fields, if needed. <p>
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The <CODE>MyDialog</CODE> class is the container for our main
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window. Initialization is again done by first calling the base class
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<CODE>__init__</CODE> function and finally setting two local variables
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that are used by <CODE>updatestatus()</CODE> later. <p>
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<CODE>Do_itemhit()</CODE> is called when an item is selected in this
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dialog by the user. We are passed the item number (and the original
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event structure, which we normally ignore). The code is similar to the
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main loop of our previous example program: a switch depending on the
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item selected. <CODE>Connect()</CODE> and <CODE>disconnect()</CODE>
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are again quite similar to our previous example. <p>
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<CODE>Updatestatus()</CODE> is different, however. It is now
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potentially called many times per second instead of only when the
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user presses a button we don't want to update the display every time
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since that would cause some quite horrible flashing. Luckily,
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<CODE>interslip.status()</CODE> not only provides us with a state and
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a message but also with a message sequence number. If neither state
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nor message sequence number has changed since the last call there is
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no need to update the display, so we just return. For the rest,
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nothing has changed. <p>
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<H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
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Now let us try to turn the python script into an applet, a standalone
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application. This will <em>not</em> work if you have the "classic 68k"
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Python distribution, only if you have the cfm68k or PPC distribution.
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<blockquote>
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Actually, "standalone" is probably not the correct term here, since an
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applet does still depend on a lot of the python environment: the
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PythonCore shared library, the Python Preferences file, the python Lib
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folder and any other modules that the main module depends on. It is
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possible to get rid of all these dependencies and create true standalone
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applications in Python, but this is a bit difficult. See <a href="standalone.html">
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Standalone Applications in Python</a> for details. For this
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document, by standalone we mean here that
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the script has the look-and-feel of an application, including the
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ability to have its own document types, be droppable, etc.
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</blockquote>
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The easiest way to create an applet is to take your source file and
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drop it onto "BuildApplet", located in the Python home
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folder. This will create an applet with the same name as your python
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source with the ".py" stripped. Also, if a resource file with the same
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name as your source but with ".rsrc" extension is available the
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resources from that file will be copied to your applet too. If there
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is no resource file for your script a set of default resources will be
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used, and the applet will have the default creator 'Pyt0'. The latter
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also happens if you do have a resource file but without the BNDL
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combo. <A NAME="no-bundle">Actually</A>, for our example that would
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have been the most logical solution, since our applet does not have
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its own data files. It would have saved us hunting for an unused
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creator code. The only reason for using the BNDL in this case is
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having the custom icon, but that could have been done by pasting an
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icon on the finder Info window, or by providing an custon icon in your
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resource file and setting the "custom icon" finder bit. <p>
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If you need slightly more control over the BuildApplet process you can
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double-click it, and you will get dialogs for source and
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destination of the applet. The rest of the process, including locating
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the resource file, remains the same. <p>
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Note that though our example application completely bypasses the
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normal python user interface this is by no means necessary. Any python
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script can be turned into an applet, and all the usual features of the
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interpreter still work. <p>
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That's all for this example, you may now return to the <A HREF="index.html">
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table of contents</A> to pick another topic. <p>
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