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Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	1	<HTML><HEAD><TITLE>Using python to create Macintosh applications, part one</TITLE></HEAD>
				2	<BODY>
				3	<H1>Using python to create Macintosh applications, part one</H1>
				4	<HR>
				5
				6	This document will show you how to create a simple mac-style
				7	application using Python. We will glance at how to use dialogs and
				8	resources. <p>
				9
				10	The example application we look at will be a simple program with a
				11	dialog that allows you to control and monitor InterSLIP, a device
				12	driver that connects your mac to the Internet via a modem connection.
				13	<A HREF="example1/InterslipControl-1.py">Source</A> and resource file
				14	(in binary and <A
				15	HREF="example1/InterslipControl-1.rsrc.hqx">BinHex</A> form for
				16	downloading) for this application are available in the <A
				17	HREF="example1">example1</A> folder (which you will have to download
				18	if you are reading this document over the net and if you want to look
				19	at the resources). <p>
				20
				21	We will use a C extension module module "interslip" that allows a
				22	Python program to control and monitor the behaviour of the low-level
				23	driver, and we will create the user interface around that. If you want
				24	to actually run the code, you will obvously need InterSLIP and the
				25	interslip module. The latter is available as a dynamically loadable
Jack Jansen	a2139fe	1998-02-25 15:40:35 +0000	[diff] [blame^]	26	extension for PowerPC/cfm68k Pythons, and may be compiled in your static 68K
				27	Python. As of this writing there is still a slight
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	28	problem with the Python interslip module causing it to say "file not
				29	found" if the driver is not loaded yet. The workaround is to load the
				30	driver by starting InterSLIP Control and quitting it. <p>
				31
				32	<CITE>
				33	If you are interested in building your own extensions to python you
				34	should check out the companion document <A
				35	HREF="plugins.html">Creating Macintosh Python C extensions</A>,
				36	which tells you how to build your own C extension. Not completely
				37	coincidental this document uses the interslip module that we will use
				38	here as an example. <p>
				39	</CITE>
				40
				41	<H2><A NAME="dialog-resources">Creating dialog resources</A></H2>
				42
				43	Let us start with the creative bit: building the dialogs and creating
				44	an icon for our program. For this you need ResEdit, and a reasonable
				45	working knowledge of how to use it. "Inside Mac" or various books on
				46	macintosh programming will help here. <p>
				47
				48	There is one fine point that deserves to be mentioned here: <A
				49	NAME="resource-numbering">resource numbering</A>. Because often your
				50	resources will be combined with those that the Python interpreter and
				51	various standard modules need you should give your DLOG and DITL
				52	resources numbers above 512. 128 and below are reserved for Apple,
Jack Jansen	a2139fe	1998-02-25 15:40:35 +0000	[diff] [blame^]	53	128-228 are for extensions like Tk,
				54	228-255 for the Python interpreter and 256-511 for standard
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	55	modules. If you are writing a module that you will be distributing for
				56	inclusion in other people's programs you may want to register a number
				57	in the 256-511 range, contact Guido or myself or whoever you think is
				58	"in charge" of Python for the Macintosh at the moment. Even though the
				59	application we are writing at the moment will keep its resources in a
				60	separate resource file it is still a good idea to make sure that no
				61	conflicts arise: once you have opened your resource file any attempt
				62	by the interpreter to open a dialog will also search your resource
				63	file. <p>
				64
				65	Okay, let's have a look at InterslipControl-1.rsrc, our resource file.
				66	The DLOG and accompanying DITL resource both have number 512. Since
				67	ResEdit creates both with default ID=128 you should take care to
				68	change the number on both. The dialog itself is pretty basic: four
				69	buttons (connect, disconnect, update status and quit), two labels and
				70	two status fields. <p>
				71
				72	<H2><A NAME="modal-dialog">An application with a modal dialog</A></H2>
				73
				74	Next, we will have to write the actual application. For this example,
				75	we will use a modal dialog. This means that we will put up the dialog
				76	and go into a loop asking the dialog manager for events (buttons
				77	pushed). We handle the actions requested by the user until the quit
				78	button is pressed, upon which we exit our loop (and the program). This
				79	way of structuring your program is actually rather antisocial, since
				80	you force the user to do whatever you, the application writer, happen
				81	to want. A modal dialog leaves no way of escape whatsoever (except
				82	command-option-escape), and is usually not a good way to structure
				83	anything but the most simple questions. Even then: how often have you
				84	been confronted with a dialog asking a question that you could not
				85	answer because the data you needed was obscured by the dialog itself?
				86	In the next example we will look at an application that does pretty
				87	much the same as this one but in a more user-friendly way. <p>
				88
				89	On to the code itself, in file <A
				90	HREF="example1/InterslipControl-1.py"> InterslipControl-1.py</A>. Have
				91	a copy handy before you read on. The file starts off with a
				92	textstring giving a short description. Not many tools do anything with
				93	this as yet, but at some point in the future we <EM>will</EM> have all
				94	sorts of nifty class browser that will display this string, so just
				95	include it. Just put a short description at the start of each module,
				96	class, method and function. After the initial description and some
				97	comments, we import the modules we need. <p>
				98
				99	<A NAME="easydialogs"><CODE>EasyDialogs</CODE></A> is a handy standard
				100	module that provides you with routines that put up common text-only
				101	modal dialogs:
				102	<UL>
				103	<LI> <CODE>Message(str)</CODE>
				104	displays the message "str" and an OK button,
				105	<LI> <CODE>AskString(prompt, default)</CODE>
				106	asks for a string, displays OK and Cancel buttons,
				107	<LI> <CODE>AskYesNoCancel(question, default)</CODE>
				108	displays a question and Yes, No and Cancel buttons.
				109	</UL>
				110
				111	<A NAME="res"><CODE>Res</CODE></A> is a pretty complete interface to
				112	the MacOS Resource Manager, described fully in Inside Mac. There is
				113	currently no documentation of it, but the Apple documentation (or
				114	Think Ref) will help you on your way if you remember two points:
				115	<UL>
				116	<LI> Resources are implemented as Python objects, and each routine
				117	with a resource first argument is implemented as a python method.
				118	<LI> When in doubt about the arguments examine the routines docstring,
				119	as in <CODE>print Res.OpenResFile.__doc__</CODE>
				120	</UL>
				121
				122	Similarly, <A NAME="dlg"><CODE>Dlg</CODE></A> is an interface to the
				123	Dialog manager (with Dialogs being implemented as python objects and
				124	routines with Dialog arguments being methods). The sys module you
				125	know, I hope. <A NAME="interslip"><CODE>Interslip</CODE></A>,
				126	finally, is the module with the interface to the InterSLIP driver. We
				127	use four calls from it:
				128	<UL>
				129	<LI> <CODE>open()</CODE>
				130	opens the driver
				131	<LI> <CODE>connect()</CODE>
				132	asks it to initiate a connection procedure (without waiting)
				133	<LI> <CODE>disconnect()</CODE>
				134	asks it to initiate a disconnection procedure (without waiting)
				135	<LI> <CODE>status()</CODE>
				136	returns the current connection status in the form of an integer state,
				137	an integer "message sequence number" and a message string.
				138	</UL>
				139
				140	Next in the source file we get definitions for our dialog resource
				141	number and for the item numbers in our dialog. These should match the
				142	situation in our resource file InterslipControl-1.rsrc,
				143	obviously. Then we get an array converting numeric state codes
				144	returned by <CODE>interslip.status()</CODE> to textual messages. <p>
				145
				146	On to the main program. We start off with opening our resource file,
				147	which should live in the same folder as the python source. If we
				148	cannot open it we use <CODE>EasyDialogs</CODE> to print a message and
				149	exit. You can try it: just move the resource file somewhere else for a
				150	moment. Then, we try to open the interslip driver, again catching an
				151	error. All modules that raise <A NAME="macos-errors">MacOS error
				152	exceptions</A> will pass a 2-tuple to the exception handler with the
				153	first item being the numeric <CODE>OSErr</CODE> code and the second
				154	one being an informative message. If no informative message is
				155	available it will be the rather uninformative <CODE>"MacOS Error
				156	-12345"</CODE>, but at least the second item will always be a
				157	printable string. Finally we call do_dialog() to do the real work. <p>
				158
				159	<CODE>Do_dialog()</CODE> uses <CODE>Dlg.GetNewDialog()</CODE> to open
				160	a dialog window initialized from 'DLOG' resource ID_MAIN and putting
				161	it on screen in the frontmost position. Next, we go into a loop,
				162	calling <CODE>Dlg.ModalDialog()</CODE> to wait for the next user
				163	action. <CODE>ModalDialog()</CODE> will return us the item number that
				164	the user has clicked on (or otherwise activated). It will handle a few
				165	slightly more complicated things also, like the user typing into
				166	simple textfields, but it will <EM>not</EM> do things like updating
				167	the physical appearance of radio buttons, etc. See Inside Mac or
				168	another programming guide for how to handle this
				169	yourself. Fortunately, our simple application doesn't have to bother
				170	with this, since buttons are the only active elements we have. So, we
				171	do a simple switch on item number and call the appropriate routine to
				172	implement the action requested. Upon the user pressing "quit" we
				173	simply leave the loop and, hence, <CODE>do_dialog()</CODE>. This will
				174	cause the python dialog object <CODE>my_dlg</CODE> to be deleted and
				175	the on-screen dialog to disappear. <p>
				176
				177	<A NAME="dialog-warning">Time for a warning</A>: be very careful what
				178	you do as long as a dialog is on-screen. Printing something, for
				179	instance, may suddenly cause the standard output window to appear over
				180	the dialog, and since we took no measures to redraw the dialog it will
				181	become very difficult to get out of the dialog. Also, command-period
				182	may or may not work in this situation. I have also seen crashes in
				183	such a situation, probably due to the multiple event loops involved or
				184	some oversight in the interpreter. You have been warned. <p>
				185
				186	The implementation of the "update status" command can use a bit more
				187	explaining: we get the new information with <CODE>do_status()</CODE>
				188	but now we have to update the on-screen dialog to present this
				189	information to the user. The <CODE>GetDialogItem()</CODE> method of
				190	the dialog returns three bits of information about the given item: its
				191	type, its data handle and its rect (the on-screen <CODE>x,y,w,h</CODE>
				192	coordinates). We are only interested in the data handle here, on which
				193	we call <CODE>SetDialogItemText()</CODE> to set our new text. Note
				194	here that python programmers need not bother with the C-string versus
				195	pascal-string controversy: the python glue module knows what is needed
				196	and converts the python string to the correct type. <p>
				197
				198	Finally, the three implementation routines <CODE>do_connect()</CODE>,
				199	<CODE>do_disconnect()</CODE> and <CODE>do_status()</CODE> are simply
				200	boring wrappers around the corresponding interslip methods that will
				201	put up a dialog in case of an error. <p>
				202
				203	And that concludes our first example of the use of resources and
				204	dialogs. Next, you could have a look at the source of EasyDialogs for
				205	some examples of using input fields and filterprocs. Or, go on with
				206	reading the <A HREF="example2.html">second part</A> of this document
				207	to see how to implement a better version of this application. Not only
				208	will it allow the user to go back to the finder (or other apps) when
				209	your application is running, it will also free her of the RSI-inducing
				210	chore of pressing "update status" continuously... <p>
				211
				212