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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. <A
HREF="example2/InterslipControl-2.py">Source</A> and resource file (in
binary and <A HREF="example2/InterslipControl-2.rsrc.hqx">BinHex</A>
form for downloading) are available in the folder <A
HREF="example2">example2</A>. If you want to run the program on your
machine you will also need a new copy of <A
HREF="update-to-1.3/FrameWork.py">FrameWork.py</A>, which has been
updated since the 1.3 release. <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, and we
provide the <A NAME="bundle">BNDL resource</A> and related stuff that
an application cannot be without. (Actually, a python applet can be
without, <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>
Let's have a look at InterslipControl-2.rsrc, our resource file. First
off, there's the standard BNDL combo. I've picked 'PYTi' as signature
for the application. I tend to pick PYT plus one lower-case letter for
my signatures. The finder gets confused if you have two applications
with the same signature. This may be due to some incorrectness on the
side of "mkapplet", 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>
There's little to tell about the BNDL stuff: I basically copied the
generic Python applet icons and pasted in the symbol for
InterSLIP. The two dialogs are equally unexciting: dialog 512 is our
main window which has four static text fields (two of which we will be
modifying during runtime, to show the status of the connection) and
two buttons "connect" and "disconnect". The "quit" and "update status"
buttons have disappeared, because they are handled by a menu choice
and automatically, respectively. <p>
<H2>A modeless dialog application using FrameWork</H2>
On to the source code in <A
HREF="example2/InterslipControl-2.py">InterslipControl-2.py</A>. The
start is similar to our previous example program <A
HREF="example1/InterslipControl-1.py">InterSlipControl-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>
<CITE>
A more complete description of <A NAME="framework">FrameWork</A> is
sorely needed, and will (at some point) be incorporated in the
programmers manual or in place of this paragraph. For now you'll have
to make do with the knowledge that you use FrameWork by building your
classes upon the classes provided by it and selectively overriding
methods to extend its functionality (or override the default
behaviour). And you should read the Source, of Course:-) <p>
</CITE>
After the imports we get the definitions of resource-IDs in our
resource file, slightly changed from the previous version of our
program, and the state to string mapping. 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>InterslipControl</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 <CODE>self</CODE> is
raised, 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, raises 'self' which
causes the mainloop to terminate. <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>
Our main object finally overrides <CODE>idle()</CODE>, the method
called when no event is available. It passes the call on to our dialog
object to give it a chance to update the status fields, if needed. <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 two local variables
that are used by <CODE>updatestatus()</CODE> later. <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>Connect()</CODE> and <CODE>disconnect()</CODE>
are again quite similar to our previous example. <p>
<CODE>Updatestatus()</CODE> is different, however. It is now
potentially called many times per second instead of only when the
user presses a button we don't want to update the display every time
since that would cause some quite horrible flashing. Luckily,
<CODE>interslip.status()</CODE> not only provides us with a state and
a message but also with a message sequence number. If neither state
nor message sequence number has changed since the last call there is
no need to update the display, so we just return. For the rest,
nothing has changed. <p>
<H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
Now, if you have a PowerPC Macintosh, let us try to turn the python
script into an applet, a standalone application. 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 except for the dependency on
PythonCore, but at the moment that is still quite difficult so we will
ignore that possibility for now. 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. <p>
The easiest way to create an applet is to take your source file and
drop it onto "mkapplet" (normally 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 'PYTa'. The latter
also happens if you do have a resource file but without the BNDL
combo. <A NAME="no-bundle">Actually</A>, for our example that would
have been the most logical solution, since our applet does not have
its own data files. It would have saved us hunting for an unused
creator code. The only reason for using the BNDL in this case is
having the custom icon, but that could have been done by pasting an
icon on the finder Info window, or by providing an custon icon in your
resource file and setting the "custom icon" finder bit. <p>
If you need slightly more control over the mkapplet process you can
double-click mkapplet, 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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