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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>
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	3
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	4	<H1>Using python to create Macintosh applications, part one</H1>
				5	<HR>
				6
				7	This document will show you how to create a simple mac-style
				8	application using Python. We will glance at how to use dialogs and
				9	resources. <p>
				10
				11	The example application we look at will be a simple program with a
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	12	dialog that allows you to perform domain name lookups on IP addresses
				13	and hostnames.
				14	The <A HREF="example1/dnslookup-1.py">source code</A> and
				15	<A HREF="example1/dnslookup-1.rsrc">resource file</A>
				16	for this application are available in the <A
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	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
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	21	We will use the builtin module "socket" that allows a
				22	Python program to perform all sorts of networking functions, and we
				23	will create the user interface around that. You should be able to run
				24	the sample code with the standard Python distribution.<p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	25
				26	<CITE>
				27	If you are interested in building your own extensions to python you
				28	should check out the companion document <A
				29	HREF="plugins.html">Creating Macintosh Python C extensions</A>,
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	30	which tells you how to build your own C extension.
				31	<p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	32	</CITE>
				33
				34	<H2><A NAME="dialog-resources">Creating dialog resources</A></H2>
				35
				36	Let us start with the creative bit: building the dialogs and creating
				37	an icon for our program. For this you need ResEdit, and a reasonable
				38	working knowledge of how to use it. "Inside Mac" or various books on
				39	macintosh programming will help here. <p>
				40
				41	There is one fine point that deserves to be mentioned here: <A
				42	NAME="resource-numbering">resource numbering</A>. Because often your
				43	resources will be combined with those that the Python interpreter and
				44	various standard modules need you should give your DLOG and DITL
				45	resources numbers above 512. 128 and below are reserved for Apple,
Jack Jansen	a2139fe	1998-02-25 15:40:35 +0000	[diff] [blame]	46	128-228 are for extensions like Tk,
				47	228-255 for the Python interpreter and 256-511 for standard
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	48	modules. If you are writing a module that you will be distributing for
				49	inclusion in other people's programs you may want to register a number
				50	in the 256-511 range, contact Guido or myself or whoever you think is
				51	"in charge" of Python for the Macintosh at the moment. Even though the
				52	application we are writing at the moment will keep its resources in a
				53	separate resource file it is still a good idea to make sure that no
				54	conflicts arise: once you have opened your resource file any attempt
				55	by the interpreter to open a dialog will also search your resource
				56	file. <p>
				57
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	58	Okay, let's have a look at dnslookup-1.rsrc, our resource file.
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	59	The DLOG and accompanying DITL resource both have number 512. Since
				60	ResEdit creates both with default ID=128 you should take care to
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	61	change the number on both. The dialog itself is pretty basic: two
				62	buttons (Lookup and Quit), two labels and
				63	two text entry areas, one of which is used for output only. Here's what
				64	the dialog will look like at run time<p>
				65	<div align=center>
				66	<img width=324 height=189 src="example1/dnslookup-1.gif" alt="dialog image">
				67	</div>
				68	<p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	69
				70	<H2><A NAME="modal-dialog">An application with a modal dialog</A></H2>
				71
				72	Next, we will have to write the actual application. For this example,
				73	we will use a modal dialog. This means that we will put up the dialog
				74	and go into a loop asking the dialog manager for events (buttons
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	75	pushed). We handle the actions requested by the user until the Quit
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	76	button is pressed, upon which we exit our loop (and the program). This
				77	way of structuring your program is actually rather antisocial, since
				78	you force the user to do whatever you, the application writer, happen
				79	to want. A modal dialog leaves no way of escape whatsoever (except
				80	command-option-escape), and is usually not a good way to structure
				81	anything but the most simple questions. Even then: how often have you
				82	been confronted with a dialog asking a question that you could not
				83	answer because the data you needed was obscured by the dialog itself?
				84	In the next example we will look at an application that does pretty
				85	much the same as this one but in a more user-friendly way. <p>
				86
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	87	The code itself is contained in the file <A
				88	HREF="example1/dnslookup-1.py"> dnslookup-1.py</A>. Have
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	89	a copy handy before you read on. The file starts off with a
				90	textstring giving a short description. Not many tools do anything with
				91	this as yet, but at some point in the future we <EM>will</EM> have all
				92	sorts of nifty class browser that will display this string, so just
				93	include it. Just put a short description at the start of each module,
				94	class, method and function. After the initial description and some
				95	comments, we import the modules we need. <p>
				96
				97	<A NAME="easydialogs"><CODE>EasyDialogs</CODE></A> is a handy standard
				98	module that provides you with routines that put up common text-only
				99	modal dialogs:
				100	<UL>
				101	<LI> <CODE>Message(str)</CODE>
				102	displays the message "str" and an OK button,
				103	<LI> <CODE>AskString(prompt, default)</CODE>
				104	asks for a string, displays OK and Cancel buttons,
				105	<LI> <CODE>AskYesNoCancel(question, default)</CODE>
				106	displays a question and Yes, No and Cancel buttons.
				107	</UL>
				108
				109	<A NAME="res"><CODE>Res</CODE></A> is a pretty complete interface to
				110	the MacOS Resource Manager, described fully in Inside Mac. There is
				111	currently no documentation of it, but the Apple documentation (or
				112	Think Ref) will help you on your way if you remember two points:
				113	<UL>
				114	<LI> Resources are implemented as Python objects, and each routine
				115	with a resource first argument is implemented as a python method.
				116	<LI> When in doubt about the arguments examine the routines docstring,
				117	as in <CODE>print Res.OpenResFile.__doc__</CODE>
				118	</UL>
				119
				120	Similarly, <A NAME="dlg"><CODE>Dlg</CODE></A> is an interface to the
				121	Dialog manager (with Dialogs being implemented as python objects and
				122	routines with Dialog arguments being methods). The sys module you
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	123	know, I hope. The string module is an often used module that enables
				124	you to perform many string related operations. In this case however, we
				125	are only using the "digits" constant from the string module. We could
				126	have simply defined "digits" as "0123456789". The socket module enables
				127	us to perform the domain name lookups. We
				128	use two calls from it:
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	129	<UL>
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	130	<LI> <CODE>gethostbyaddr()</CODE>
				131	returns the hostname associated with an IP address
				132	<LI> <CODE>gethostbyname()</CODE>
				133	returns the IP address associated with a hostname
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	134	</UL>
				135
				136	Next in the source file we get definitions for our dialog resource
				137	number and for the item numbers in our dialog. These should match the
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	138	situation in our resource file dnslookup-1.rsrc,
				139	obviously.<p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	140
				141	On to the main program. We start off with opening our resource file,
				142	which should live in the same folder as the python source. If we
				143	cannot open it we use <CODE>EasyDialogs</CODE> to print a message and
				144	exit. You can try it: just move the resource file somewhere else for a
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	145	moment. Then we call do_dialog() to do the real work. <p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	146
				147	<CODE>Do_dialog()</CODE> uses <CODE>Dlg.GetNewDialog()</CODE> to open
				148	a dialog window initialized from 'DLOG' resource ID_MAIN and putting
				149	it on screen in the frontmost position. Next, we go into a loop,
				150	calling <CODE>Dlg.ModalDialog()</CODE> to wait for the next user
				151	action. <CODE>ModalDialog()</CODE> will return us the item number that
				152	the user has clicked on (or otherwise activated). It will handle a few
				153	slightly more complicated things also, like the user typing into
				154	simple textfields, but it will <EM>not</EM> do things like updating
				155	the physical appearance of radio buttons, etc. See Inside Mac or
				156	another programming guide for how to handle this
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	157	yourself. Fortunately, our simple application doesn't have to bother with this,
				158	since buttons and textfields are the only active elements we have. So, we do a
				159	simple switch on item number and call the appropriate routine to implement the
				160	action requested. Upon the user pressing "Quit" we simply leave the loop and,
				161	hence, <CODE>do_dialog()</CODE>. This will cause the python dialog object
				162	<CODE>my_dlg</CODE> to be deleted and the on-screen dialog to disappear. <p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	163
				164	<A NAME="dialog-warning">Time for a warning</A>: be very careful what
				165	you do as long as a dialog is on-screen. Printing something, for
				166	instance, may suddenly cause the standard output window to appear over
				167	the dialog, and since we took no measures to redraw the dialog it will
				168	become very difficult to get out of the dialog. Also, command-period
				169	may or may not work in this situation. I have also seen crashes in
				170	such a situation, probably due to the multiple event loops involved or
				171	some oversight in the interpreter. You have been warned. <p>
				172
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	173	The implementation of the "Lookup" command can use a bit more
				174	explaining: we get the necessary information with <CODE>dnslookup()</CODE>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	175	but now we have to update the on-screen dialog to present this
				176	information to the user. The <CODE>GetDialogItem()</CODE> method of
				177	the dialog returns three bits of information about the given item: its
				178	type, its data handle and its rect (the on-screen <CODE>x,y,w,h</CODE>
				179	coordinates). We are only interested in the data handle here, on which
				180	we call <CODE>SetDialogItemText()</CODE> to set our new text. Note
				181	here that python programmers need not bother with the C-string versus
				182	pascal-string controversy: the python glue module knows what is needed
				183	and converts the python string to the correct type. <p>
				184
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	185	And that concludes our first example of the use of resources and
				186	dialogs. Next, you could have a look at the source of EasyDialogs for
				187	some examples of using input fields and filterprocs. Or, go on with
				188	reading the <A HREF="example2.html">second part</A> of this document
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	189	to see how to implement a better version of this application.<p>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	190
Jack Jansen	2450a25	1999-12-03 15:15:28 +0000	[diff] [blame]	191	</BODY>
				192	</HTML>
Jack Jansen	a630813	1996-03-18 13:38:52 +0000	[diff] [blame]	193