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  1<HTML><HEAD><TITLE>Using python to create Macintosh applications, part two</TITLE></HEAD>
  2<BODY>
  3<H1>Using python to create Macintosh applications, part two</H1>
  4<HR>
  5
  6In this document we rewrite the application of the <A
  7HREF="example1.html">previous example</A> to use modeless dialogs. We
  8will use an application framework, and we will have a look at creating
  9applets, standalone applications written in Python.  The <A
 10HREF="example2/dnslookup-2.py">source code</A> and 
 11<A HREF="example2/dnslookup-2.rsrc">resource file</A> are available in the folder 
 12<A HREF="example2">example2</A>. <p>
 13
 14Again, we start with ResEdit to create our dialogs. Not only do we
 15want a main dialog this time but also an "About" dialog.  This example is less
 16than complete since we do not provide a <A NAME="bundle">BNDL resource</A> 
 17and related stuff that an application cannot be without. We are able to do this
 18when building a python applet since BuildApplet will substitute default resources
 19for BNDL, etc. when none are supplied (<A HREF="#no-bundle">See below</A>.)
 20"Inside Mac" or various
 21books on Macintosh programming will help here. Also, you can refer to
 22the resource files provided in the Python source distribution for some
 23of the python-specific points of BNDL programming: the
 24"appletbundle.rsrc" file is what is used for creating applets if you
 25don't provide your own resource file. <p>
 26
 27When creating your own BNDL resouorces, keep in mind that the Finder gets 
 28confused if you have more than one application with the same signature. This may be due 
 29to some incorrectness on the side of "BuildApplet", I am not sure.  There is one 
 30case when you definitely need a unique signature: when you create an applet that 
 31has its own data files and you want the user to be able to start your
 32applet by double-clicking one of the datafiles. <p>
 33
 34Let's have a look at dnslookup-2.rsrc, our resource file. Dialog 512 is the
 35main window which has one button (Lookup), two labels and
 36two text entry areas, one of which is used for output only. The "Quit"
 37button has disappeared, because its function is handled by a menu choice.  Here's
 38what it will look like at run time:<p>
 39<div align=center>
 40<img width=324 height=205 src="example2/dnslookup-2.gif" alt="dialog image">
 41</div>
 42<p>
 43
 44<H2>A modeless dialog application using FrameWork</H2>
 45
 46On to the source code in <A
 47HREF="example2/dnslookup-2.py">dnslookup-2.py</A>.  The
 48start is similar to our previous example program <A
 49HREF="example1/dnslookup-1.py">dnslookup-1.py</A>, with
 50one extra module being imported. To make life more simple we will use
 51the <CODE>FrameWork</CODE> module, a nifty piece of code that handles
 52all the gory Mac details of event loop programming, menubar
 53installation and all the other code that is the same for every Mac
 54program in the world.  Like most standard modules, FrameWork will run
 55some sample test code when you invoke it as a main program, so try it
 56now. It will create a menu bar with an Apple menu with the about box
 57and a "File" menu with some pythonesque choices (which do nothing
 58interesting, by the way) and a "Quit" command that works. <p>
 59
 60<BLOCKQUOTE>
 61If you have not used <code>FrameWork</code> before you may want to
 62first take a look at the <A HREF="textedit.html">Pathetic EDitor</A>
 63example, which builds a minimal text editor using FrameWork and TextEdit.
 64On the other hand: we don't use many features of FrameWork, so you could
 65also continue with this document. 
 66</BLOCKQUOTE>
 67
 68After the imports we get the definitions of resource-IDs in our
 69resource file, slightly changed from the previous version of our
 70program. The main program is also
 71similar to our previous version, with one important exception: we
 72first check to see whether our resource is available before opening
 73the resource file. Why is this? Because later, when we will have
 74converted the script to an applet, our resources will be available in
 75the applet file and we don't need the separate resource file
 76anymore. <p>
 77
 78Next comes the definition of our main class,
 79<CODE>DNSLookup</CODE>, which inherits
 80<CODE>FrameWork.Application</CODE>. The Application class handles the
 81menu bar and the main event loop and event dispatching. In the
 82<CODE>__init__</CODE> routine we first let the base class initialize
 83itself, then we create our modeless dialog and finally we jump into
 84the main loop. The main loop continues until we call <CODE>self._quit</CODE>,
 85which we will do when the user selects "Quit". When we create
 86the instance of <CODE>MyDialog</CODE> (which inherits
 87<CODE>DialogWindow</CODE>, which inherits <CODE>Window</CODE>) we pass
 88a reference to the application object, this reference is used to tell
 89Application about our new window.  This enables the event loop to keep
 90track of all windows and dispatch things like update events and mouse
 91clicks. <p>
 92
 93The <CODE>makeusermenus()</CODE> method (which is called sometime
 94during the Application <CODE>__init__</CODE> routine) creates a File
 95menu with a Quit command (shortcut command-Q), which will callback to
 96our quit() method. <CODE>Quit()</CODE>, in turn, calls <CODE>_quit</CODE> which
 97causes the mainloop to terminate at a convenient time. <p>
 98
 99Application provides a standard about box, but we override this by
100providing our own <CODE>do_about()</CODE> method which shows an about
101box from a resource as a modal dialog. This piece of code should look
102familiar to you from the previous example program. That do_about is
103called when the user selects About from the Apple menu is, again,
104taken care of by the __init__ routine of Application. <p>
105
106The <CODE>MyDialog</CODE> class is the container for our main
107window. Initialization is again done by first calling the base class
108<CODE>__init__</CODE> function and finally setting the local variable
109"parent." <p>
110
111<CODE>Do_itemhit()</CODE> is called when an item is selected in this
112dialog by the user. We are passed the item number (and the original
113event structure, which we normally ignore). The code is similar to the
114main loop of our previous example program: a switch depending on the
115item selected.  <CODE>Dnslookup()</CODE> is quite similar to our previous 
116example. <p>
117
118<H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
119
120Now let us try to turn the python script into an applet, a standalone
121application. This will <em>not</em> work if you have the "classic 68k"
122Python distribution, only if you have the cfm68k or PPC distribution.
123
124<blockquote>
125Actually, "standalone" is probably not the correct term here, since an
126applet does still depend on a lot of the python environment: the
127PythonCore shared library, the Python Preferences file, the python Lib
128folder and any other modules that the main module depends on. It is
129possible to get rid of all these dependencies and create true standalone
130applications in Python, but this is a bit difficult. See <a href="freezing.html">
131Standalone Applications in Python</a> for details. For this
132document, by standalone we mean here that
133the script has the look-and-feel of an application, including the
134ability to have its own document types, be droppable, etc.
135</blockquote>
136
137The easiest way to create an applet is to take your source file and
138drop it onto "BuildApplet", located in the Python home
139folder. This will create an applet with the same name as your python
140source with the ".py" stripped. Also, if a resource file with the same
141name as your source but with ".rsrc" extension is available the
142resources from that file will be copied to your applet too. If there
143is no resource file for your script a set of default resources will be
144used, and the applet will have the default creator 'Pyt0'. The latter
145also happens if you do have a resource file but without the BNDL
146combo. <A NAME="no-bundle">Actually</A>, as in the present example.
147<p>
148
149If you need slightly more control over the BuildApplet process you can
150double-click it, and you will get dialogs for source and
151destination of the applet. The rest of the process, including locating
152the resource file, remains the same. <p>
153
154Note that though our example application completely bypasses the
155normal python user interface this is by no means necessary. Any python
156script can be turned into an applet, and all the usual features of the
157interpreter still work. <p>
158
159That's all for this example, you may now return to the <A HREF="index.html">
160table of contents</A> to pick another topic. <p>
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