mirror of https://github.com/python/cpython.git
212 lines
11 KiB
HTML
212 lines
11 KiB
HTML
|
<HTML><HEAD><TITLE>Using python to create Macintosh applications, part one</TITLE></HEAD>
|
||
|
|
<BODY>
|
||
|
|
<H1>Using python to create Macintosh applications, part one</H1>
|
||
|
|
<HR>
|
||
|
|
|
||
|
|
This document will show you how to create a simple mac-style
|
||
|
|
application using Python. We will glance at how to use dialogs and
|
||
|
|
resources. <p>
|
||
|
|
|
||
|
|
The example application we look at will be a simple program with a
|
||
|
|
dialog that allows you to control and monitor InterSLIP, a device
|
||
|
|
driver that connects your mac to the Internet via a modem connection.
|
||
|
|
<A HREF="example1/InterslipControl-1.py">Source</A> and resource file
|
||
|
|
(in binary and <A
|
||
|
|
HREF="example1/InterslipControl-1.rsrc.hqx">BinHex</A> form for
|
||
|
|
downloading) for this application are available in the <A
|
||
|
|
HREF="example1">example1</A> folder (which you will have to download
|
||
|
|
if you are reading this document over the net and if you want to look
|
||
|
|
at the resources). <p>
|
||
|
|
|
||
|
|
We will use a C extension module module "interslip" that allows a
|
||
|
|
Python program to control and monitor the behaviour of the low-level
|
||
|
|
driver, and we will create the user interface around that. If you want
|
||
|
|
to actually run the code, you will obvously need InterSLIP and the
|
||
|
|
interslip module. The latter is available as a dynamically loadable
|
||
|
|
extension for PowerPC macs, and may be compiled in your Python
|
||
|
|
interpreter for 68K macs. As of this writing there is still a slight
|
||
|
|
problem with the Python interslip module causing it to say "file not
|
||
|
|
found" if the driver is not loaded yet. The workaround is to load the
|
||
|
|
driver by starting InterSLIP Control and quitting it. <p>
|
||
|
|
|
||
|
|
<CITE>
|
||
|
|
If you are interested in building your own extensions to python you
|
||
|
|
should check out the companion document <A
|
||
|
|
HREF="plugins.html">Creating Macintosh Python C extensions</A>,
|
||
|
|
which tells you how to build your own C extension. Not completely
|
||
|
|
coincidental this document uses the interslip module that we will use
|
||
|
|
here as an example. <p>
|
||
|
|
</CITE>
|
||
|
|
|
||
|
|
<H2><A NAME="dialog-resources">Creating dialog resources</A></H2>
|
||
|
|
|
||
|
|
Let us start with the creative bit: building the dialogs and creating
|
||
|
|
an icon for our program. For this you need ResEdit, and a reasonable
|
||
|
|
working knowledge of how to use it. "Inside Mac" or various books on
|
||
|
|
macintosh programming will help here. <p>
|
||
|
|
|
||
|
|
There is one fine point that deserves to be mentioned here: <A
|
||
|
|
NAME="resource-numbering">resource numbering</A>. Because often your
|
||
|
|
resources will be combined with those that the Python interpreter and
|
||
|
|
various standard modules need you should give your DLOG and DITL
|
||
|
|
resources numbers above 512. 128 and below are reserved for Apple,
|
||
|
|
128-255 for the Python interpreter and 256-511 for standard
|
||
|
|
modules. If you are writing a module that you will be distributing for
|
||
|
|
inclusion in other people's programs you may want to register a number
|
||
|
|
in the 256-511 range, contact Guido or myself or whoever you think is
|
||
|
|
"in charge" of Python for the Macintosh at the moment. Even though the
|
||
|
|
application we are writing at the moment will keep its resources in a
|
||
|
|
separate resource file it is still a good idea to make sure that no
|
||
|
|
conflicts arise: once you have opened your resource file any attempt
|
||
|
|
by the interpreter to open a dialog will also search your resource
|
||
|
|
file. <p>
|
||
|
|
|
||
|
|
Okay, let's have a look at InterslipControl-1.rsrc, our resource file.
|
||
|
|
The DLOG and accompanying DITL resource both have number 512. Since
|
||
|
|
ResEdit creates both with default ID=128 you should take care to
|
||
|
|
change the number on both. The dialog itself is pretty basic: four
|
||
|
|
buttons (connect, disconnect, update status and quit), two labels and
|
||
|
|
two status fields. <p>
|
||
|
|
|
||
|
|
<H2><A NAME="modal-dialog">An application with a modal dialog</A></H2>
|
||
|
|
|
||
|
|
Next, we will have to write the actual application. For this example,
|
||
|
|
we will use a modal dialog. This means that we will put up the dialog
|
||
|
|
and go into a loop asking the dialog manager for events (buttons
|
||
|
|
pushed). We handle the actions requested by the user until the quit
|
||
|
|
button is pressed, upon which we exit our loop (and the program). This
|
||
|
|
way of structuring your program is actually rather antisocial, since
|
||
|
|
you force the user to do whatever you, the application writer, happen
|
||
|
|
to want. A modal dialog leaves no way of escape whatsoever (except
|
||
|
|
command-option-escape), and is usually not a good way to structure
|
||
|
|
anything but the most simple questions. Even then: how often have you
|
||
|
|
been confronted with a dialog asking a question that you could not
|
||
|
|
answer because the data you needed was obscured by the dialog itself?
|
||
|
|
In the next example we will look at an application that does pretty
|
||
|
|
much the same as this one but in a more user-friendly way. <p>
|
||
|
|
|
||
|
|
On to the code itself, in file <A
|
||
|
|
HREF="example1/InterslipControl-1.py"> InterslipControl-1.py</A>. Have
|
||
|
|
a copy handy before you read on. The file starts off with a
|
||
|
|
textstring giving a short description. Not many tools do anything with
|
||
|
|
this as yet, but at some point in the future we <EM>will</EM> have all
|
||
|
|
sorts of nifty class browser that will display this string, so just
|
||
|
|
include it. Just put a short description at the start of each module,
|
||
|
|
class, method and function. After the initial description and some
|
||
|
|
comments, we import the modules we need. <p>
|
||
|
|
|
||
|
|
<A NAME="easydialogs"><CODE>EasyDialogs</CODE></A> is a handy standard
|
||
|
|
module that provides you with routines that put up common text-only
|
||
|
|
modal dialogs:
|
||
|
|
<UL>
|
||
|
|
<LI> <CODE>Message(str)</CODE>
|
||
|
|
displays the message "str" and an OK button,
|
||
|
|
<LI> <CODE>AskString(prompt, default)</CODE>
|
||
|
|
asks for a string, displays OK and Cancel buttons,
|
||
|
|
<LI> <CODE>AskYesNoCancel(question, default)</CODE>
|
||
|
|
displays a question and Yes, No and Cancel buttons.
|
||
|
|
</UL>
|
||
|
|
|
||
|
|
<A NAME="res"><CODE>Res</CODE></A> is a pretty complete interface to
|
||
|
|
the MacOS Resource Manager, described fully in Inside Mac. There is
|
||
|
|
currently no documentation of it, but the Apple documentation (or
|
||
|
|
Think Ref) will help you on your way if you remember two points:
|
||
|
|
<UL>
|
||
|
|
<LI> Resources are implemented as Python objects, and each routine
|
||
|
|
with a resource first argument is implemented as a python method.
|
||
|
|
<LI> When in doubt about the arguments examine the routines docstring,
|
||
|
|
as in <CODE>print Res.OpenResFile.__doc__</CODE>
|
||
|
|
</UL>
|
||
|
|
|
||
|
|
Similarly, <A NAME="dlg"><CODE>Dlg</CODE></A> is an interface to the
|
||
|
|
Dialog manager (with Dialogs being implemented as python objects and
|
||
|
|
routines with Dialog arguments being methods). The sys module you
|
||
|
|
know, I hope. <A NAME="interslip"><CODE>Interslip</CODE></A>,
|
||
|
|
finally, is the module with the interface to the InterSLIP driver. We
|
||
|
|
use four calls from it:
|
||
|
|
<UL>
|
||
|
|
<LI> <CODE>open()</CODE>
|
||
|
|
opens the driver
|
||
|
|
<LI> <CODE>connect()</CODE>
|
||
|
|
asks it to initiate a connection procedure (without waiting)
|
||
|
|
<LI> <CODE>disconnect()</CODE>
|
||
|
|
asks it to initiate a disconnection procedure (without waiting)
|
||
|
|
<LI> <CODE>status()</CODE>
|
||
|
|
returns the current connection status in the form of an integer state,
|
||
|
|
an integer "message sequence number" and a message string.
|
||
|
|
</UL>
|
||
|
|
|
||
|
|
Next in the source file we get definitions for our dialog resource
|
||
|
|
number and for the item numbers in our dialog. These should match the
|
||
|
|
situation in our resource file InterslipControl-1.rsrc,
|
||
|
|
obviously. Then we get an array converting numeric state codes
|
||
|
|
returned by <CODE>interslip.status()</CODE> to textual messages. <p>
|
||
|
|
|
||
|
|
On to the main program. We start off with opening our resource file,
|
||
|
|
which should live in the same folder as the python source. If we
|
||
|
|
cannot open it we use <CODE>EasyDialogs</CODE> to print a message and
|
||
|
|
exit. You can try it: just move the resource file somewhere else for a
|
||
|
|
moment. Then, we try to open the interslip driver, again catching an
|
||
|
|
error. All modules that raise <A NAME="macos-errors">MacOS error
|
||
|
|
exceptions</A> will pass a 2-tuple to the exception handler with the
|
||
|
|
first item being the numeric <CODE>OSErr</CODE> code and the second
|
||
|
|
one being an informative message. If no informative message is
|
||
|
|
available it will be the rather uninformative <CODE>"MacOS Error
|
||
|
|
-12345"</CODE>, but at least the second item will always be a
|
||
|
|
printable string. Finally we call do_dialog() to do the real work. <p>
|
||
|
|
|
||
|
|
<CODE>Do_dialog()</CODE> uses <CODE>Dlg.GetNewDialog()</CODE> to open
|
||
|
|
a dialog window initialized from 'DLOG' resource ID_MAIN and putting
|
||
|
|
it on screen in the frontmost position. Next, we go into a loop,
|
||
|
|
calling <CODE>Dlg.ModalDialog()</CODE> to wait for the next user
|
||
|
|
action. <CODE>ModalDialog()</CODE> will return us the item number that
|
||
|
|
the user has clicked on (or otherwise activated). It will handle a few
|
||
|
|
slightly more complicated things also, like the user typing into
|
||
|
|
simple textfields, but it will <EM>not</EM> do things like updating
|
||
|
|
the physical appearance of radio buttons, etc. See Inside Mac or
|
||
|
|
another programming guide for how to handle this
|
||
|
|
yourself. Fortunately, our simple application doesn't have to bother
|
||
|
|
with this, since buttons are the only active elements we have. So, we
|
||
|
|
do a simple switch on item number and call the appropriate routine to
|
||
|
|
implement the action requested. Upon the user pressing "quit" we
|
||
|
|
simply leave the loop and, hence, <CODE>do_dialog()</CODE>. This will
|
||
|
|
cause the python dialog object <CODE>my_dlg</CODE> to be deleted and
|
||
|
|
the on-screen dialog to disappear. <p>
|
||
|
|
|
||
|
|
<A NAME="dialog-warning">Time for a warning</A>: be very careful what
|
||
|
|
you do as long as a dialog is on-screen. Printing something, for
|
||
|
|
instance, may suddenly cause the standard output window to appear over
|
||
|
|
the dialog, and since we took no measures to redraw the dialog it will
|
||
|
|
become very difficult to get out of the dialog. Also, command-period
|
||
|
|
may or may not work in this situation. I have also seen crashes in
|
||
|
|
such a situation, probably due to the multiple event loops involved or
|
||
|
|
some oversight in the interpreter. You have been warned. <p>
|
||
|
|
|
||
|
|
The implementation of the "update status" command can use a bit more
|
||
|
|
explaining: we get the new information with <CODE>do_status()</CODE>
|
||
|
|
but now we have to update the on-screen dialog to present this
|
||
|
|
information to the user. The <CODE>GetDialogItem()</CODE> method of
|
||
|
|
the dialog returns three bits of information about the given item: its
|
||
|
|
type, its data handle and its rect (the on-screen <CODE>x,y,w,h</CODE>
|
||
|
|
coordinates). We are only interested in the data handle here, on which
|
||
|
|
we call <CODE>SetDialogItemText()</CODE> to set our new text. Note
|
||
|
|
here that python programmers need not bother with the C-string versus
|
||
|
|
pascal-string controversy: the python glue module knows what is needed
|
||
|
|
and converts the python string to the correct type. <p>
|
||
|
|
|
||
|
|
Finally, the three implementation routines <CODE>do_connect()</CODE>,
|
||
|
|
<CODE>do_disconnect()</CODE> and <CODE>do_status()</CODE> are simply
|
||
|
|
boring wrappers around the corresponding interslip methods that will
|
||
|
|
put up a dialog in case of an error. <p>
|
||
|
|
|
||
|
|
And that concludes our first example of the use of resources and
|
||
|
|
dialogs. Next, you could have a look at the source of EasyDialogs for
|
||
|
|
some examples of using input fields and filterprocs. Or, go on with
|
||
|
|
reading the <A HREF="example2.html">second part</A> of this document
|
||
|
|
to see how to implement a better version of this application. Not only
|
||
|
|
will it allow the user to go back to the finder (or other apps) when
|
||
|
|
your application is running, it will also free her of the RSI-inducing
|
||
|
|
chore of pressing "update status" continuously... <p>
|
||
|
|
|
||
|
|
|