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<HTML><HEAD><TITLE>Using python to create Macintosh applications, part two</TITLE></HEAD>
<BODY>
<H1>Using python to create Macintosh applications, part two</H1>
<HR>
In this document we rewrite the application of the <A
HREF="example1.html">previous example</A> 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 <A
HREF="example2/dnslookup-2.py">source code</A> and
<A HREF="example2/dnslookup-2.rsrc">resource file</A> are available in the folder
<A HREF="example2">example2</A>. <p>
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 <A NAME="bundle">BNDL resource</A>
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 (<A HREF="#no-bundle">See below</A>.)
"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. <p>
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. <p>
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:<p>
<div align=center>
<img width=324 height=205 src="example2/dnslookup-2.gif" alt="dialog image">
</div>
<p>
<H2>A modeless dialog application using FrameWork</H2>
On to the source code in <A
HREF="example2/dnslookup-2.py">dnslookup-2.py</A>. The
start is similar to our previous example program <A
HREF="example1/dnslookup-1.py">dnslookup-1.py</A>, with
one extra module being imported. To make life more simple we will use
the <CODE>FrameWork</CODE> 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. <p>
<BLOCKQUOTE>
If you have not used <code>FrameWork</code> before you may want to
first take a look at the <A HREF="textedit.html">Pathetic EDitor</A>
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.
</BLOCKQUOTE>
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. <p>
Next comes the definition of our main class,
<CODE>DNSLookup</CODE>, which inherits
<CODE>FrameWork.Application</CODE>. The Application class handles the
menu bar and the main event loop and event dispatching. In the
<CODE>__init__</CODE> 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 <CODE>self._quit</CODE>,
which we will do when the user selects "Quit". When we create
the instance of <CODE>MyDialog</CODE> (which inherits
<CODE>DialogWindow</CODE>, which inherits <CODE>Window</CODE>) 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. <p>
The <CODE>makeusermenus()</CODE> method (which is called sometime
during the Application <CODE>__init__</CODE> routine) creates a File
menu with a Quit command (shortcut command-Q), which will callback to
our quit() method. <CODE>Quit()</CODE>, in turn, calls <CODE>_quit</CODE> which
causes the mainloop to terminate at a convenient time. <p>
Application provides a standard about box, but we override this by
providing our own <CODE>do_about()</CODE> 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. <p>
The <CODE>MyDialog</CODE> class is the container for our main
window. Initialization is again done by first calling the base class
<CODE>__init__</CODE> function and finally setting the local variable
"parent." <p>
<CODE>Do_itemhit()</CODE> 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. <CODE>Dnslookup()</CODE> is quite similar to our previous
example. <p>
<H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
Now let us try to turn the python script into an applet, a standalone
application. This will <em>not</em> work if you have the "classic 68k"
Python distribution, only if you have the cfm68k or PPC distribution.
<blockquote>
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 <a href="standalone.html">
Standalone Applications in Python</a> 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.
</blockquote>
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. <A NAME="no-bundle">Actually</A>, as in the present example.
<p>
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. <p>
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. <p>
That's all for this example, you may now return to the <A HREF="index.html">
table of contents</A> to pick another topic. <p>
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