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Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	1	<HTML>
				2	<HEAD>
				3	<TITLE>Using Python on the Macintosh</TITLE>
				4	</HEAD>
				5	<BODY>
				6	<H1>Using Python on the Macintosh</H1>
				7	<EM>(preliminary)</EM>
				8	<HR>
				9
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	10	This document is an introduction to using Python on the Apple
				11	Macintosh. It does not introduce the language itself, for this you
				12	should refer to the <A
				13	HREF="http://www.python.org/doc/tut/tut.html">Python Tutorial</A> by
				14	Guido van Rossum. This guide more-or-less replaces chapter two of the
				15	tutorial, and provides some additional material. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	16
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	17	The document refers to Python 1.3.3 or higher, some of the features
				18	(like setting applet options) will not work in earlier versions of
				19	Python. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	20
				21	<h2>Invoking the interpreter</h2>
				22
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	23	The name of the interpreter may differ on different installations: it
				24	may be called <CODE>Python</CODE>, <CODE>PythonPPC</CODE> (for powerpc
				25	macs) or <CODE>Python68K</CODE> (indeed, for 68K macs). It will always
				26	be recognizable by the "16 ton" icon, though. You start the
				27	interpreter in interactive mode by double-clicking it. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	28
				29	<img src="html.icons/python.gif"><p>
				30
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	31	This should give you a text window with an informative version string
				32	and a prompt, something like the following:
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	33	<PRE>
				34	Python 1.3.3 (Apr 7 1996) [CW PPC w/GUSI]
				35	Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
				36	>>>
				37	</PRE>
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	38	The version string tells you the version of Python, whether it was
				39	built for PPC or 68K macs and possibly some options used to build the
				40	interpreter. If you find a bug or have a question about how the
				41	interpreter works it is a good idea to include the version information
				42	in your message. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	43
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	44	At the prompt you can type interactive python commands. See the
				45	tutorial for more information. The interactive window works
				46	more-or-less like a Communication Toolbox or Telnet window: you type
				47	commands at the bottom and terminate them with the <EM>[return]</EM>
				48	or <EM>[enter]</EM> key. Interpreter feedback also appears at the
				49	bottom of the window, and the contents scroll as output is added. You
				50	can use copy and paste in the normal way, but be sure to paste only at
				51	the bottom of the document.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	52
				53	<h2>Creating Python scripts</h2>
				54
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	55	The Python interpreter works in a way that is different from what you
				56	would expect of a macintosh program: the interpreter is just that: an
				57	interpreter. There is no builtin editor or other development
				58	support. Hence, to create a Python script you need an external text
				59	editor. For a first script you can use any editor that can create
				60	plain, unstyled text files, such as <CODE>SimpleText</CODE>. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	61
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	62	For more serious scripts, though, it is advisable to use a programmers
				63	editor, such as <CODE>BBEdit</CODE> or <CODE>Alpha</CODE>. BBEdit is
				64	my favorite: it comes in a commercial version but also in a
				65	fully-functional free version <CODE>BBEdit Lite</CODE>. You can
				66	download it from the <A HREF="http://www.barebones.com/">BareBones</A>
				67	site. The free version will probably provide all the functionality
				68	you will ever need. Besides the standard edit facilities it has
				69	multi-file searches and many other goodies that can be very handy when
				70	editing programs. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	71
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	72	After you have created your script in the editor of your choice you
				73	drop it on the interpreter. This will start the interpreter executing
				74	the script, again with a console window in which the output appears
				75	and in which you can type input if the script requires it. Normally
				76	the interpreter will close the window and quit as soon as the script
				77	is done executing, see below under <A HREF="#startup">startup
				78	options</A> for a way to change this. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	79
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	80	It is a good idea to have the names of all your scripts end in
				81	<CODE>.py</CODE>. While this is not necessary for standalone scripts
				82	it is needed for modules, and it is probably a good idea to start the
				83	habit now. <p>
				84
				85	If you do not like to start the Python interpreter afresh for each
				86	edit-run cycle you can use the <CODE>import</CODE> statement and
				87	<CODE>reload()</CODE> function to speed things up in some cases. Here
				88	is Guido's original comment for how to do this, from the 1.1 release
				89	notes: <P>
				90
				91	<CITE>
				92
				93	Make sure the program is a module file (filename must be a Python
				94	identifier followed by '<CODE>.py</CODE>'). You can then import it
				95	when you test it for the first time. There are now three
				96	possibilities: it contains a syntax error; it gets a runtime error
				97	(unhandled exception); or it runs OK but gives wrong results. (If it
				98	gives correct results, you are done testing and don't need to read the
				99	rest of this paragraph. :-) Note that the following is not
				100	Mac-specific -- it's just that on UNIX it's easier to restart the
				101	entire script so it's rarely useful. <P>
				102
				103	Recovery from a syntax error is easy: edit the file and import it
				104	again. <P>
				105
				106	Recovery from wrong output is almost as easy: edit the file and,
				107	instead of importing it, call the function <CODE>reload()</CODE> with
				108	the module name as argument (e.g., if your module is called
				109	<CODE>foo</CODE>, type <CODE>reload(foo)</CODE>). <P>
				110
				111	Recovery from an exception is trickier. Once the syntax is correct, a
				112	'module' entry is placed in an internal table, and following import
				113	statements will not re-read the file, even if the module's
				114	initialization terminated with an error (one reason why this is done
				115	is so that mutually recursive modules are initialized only once). You
				116	must therefore force re-reading the module with <CODE>reload()</CODE>,
				117	however, if this happens the first time you try to import the module,
				118	the import statement itself has not completed, and your workspace does
				119	not know the module name (even though the internal table of moduesl
				120	does!). The trick is to first import the module again, then reload
				121	it. For instance, <CODE>import foo; reload(foo)</CODE>. Because the
				122	module object already exists internally, the import statement does not
				123	attempt to execute the module again -- it just places it in your
				124	workspace. </CITE>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	125
				126	<h2>Clickable python scripts</h2>
				127
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	128	If you create your script with the correct creator and type, creator
				129	<CODE>'Pyth'</CODE> and type <CODE>'TEXT'</CODE>, you can double-click
				130	your script and it will automatically invoke the interpreter. If you
				131	use BBEdit you can tell it about the Python file type by adding it to
				132	the "file types" sections of the preferences. Then, if you save a file
				133	for the first time you can tell BBEdit to save the file as a Python
				134	script through the "options" choice of the save dialog. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	135
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	136	The <CODE>Scripts</CODE> folder contains a script
				137	<CODE>fixfiletypes</CODE> that will recursively traverse a folder and
				138	set the correct creator and type for all files ending in
				139	<CODE>.py</CODE>. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	140
				141	<h2>Interaction with the user</h2>
				142
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	143	Normally, the interpreter will check for user input (mouse clicks,
				144	keyboard input) every once in a while, so it is possible to switch to
				145	other applications while a script runs. It is also possible to
				146	interrupt the interpreter with the standard command-period keypress,
				147	this will raise the <CODE>KeyboardInterrupt</CODE> exception. Scripts
				148	may, however, turn off this behaviour to facilitate their own event
				149	handling. Such scripts can only be killed with the
				150	command-option-escape shortcut.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	151
				152	<h2><A NAME="startup">startup options</A></h2>
				153
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	154	If the <EM>option</EM> key is depressed when Python starts executing
				155	the interpreter will bring up an options dialog thru which you can
				156	influence the way the interpreter behaves. Keep the option key
				157	depressed until the dialog comes up. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	158
				159	<img src="html.icons/options.gif"><p>
				160
				161	The options modify the interpreters behaviour in the following way:
				162	<ul>
				163	<li> the interpreter goes to interactive mode (in stead of
				164	exiting) after a script has terminated normally,
				165	<li> for every module imported a line is printed telling you where the
				166	module was loaded from,
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	167	<li> do not print the values of expressions executed as statements in
				168	an interactive python,
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	169	<li> do not buffer stdout and stderr,
				170	<li> print some debugging output during the parsing phase,
				171	<li> keep the output window open when a script terminates.
				172	</ul>
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	173	In addition, you can enter a unix-style command line which is passed
				174	to the script in <CODE>sys.argv</CODE>. Sys.argv[0] is always the name
				175	of the script being executed, additional values can be passed
				176	here. Quoting works as expected. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	177
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	178	The default options are also settable on a system-wide basis, see the
				179	section on <A HREF="#preferences">editing preferences</A>. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	180
				181	<h2>Module search path</h2>
				182
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	183	The module search path, <CODE>sys.path</CODE>, contains the folders
				184	python will search when you import a module. The path is settable on a
				185	system-wide basis (see the preferences section), and normally
				186	comprises the current folder (where the script lives), the
				187	<CODE>Lib</CODE> folder and some of its subfolders and possibly some
				188	more. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	189
				190	<h2>Working folder</h2>
				191
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	192	The unix concept of a <I>working directory</I> does not translate
				193	directly to a similar concept on the Macintosh. To facilitate easy
				194	porting and the use of relative pathnames in scripts the interpreter
				195	simulates a working directory. When a script is started the initial
				196	working directory is the folder where the script lives. In case of an
				197	interactive interpreter the working directory is the folder where the
				198	interpreter lives. <P>
				199
				200	By the way: the "standard file" folder, the folder that is presented
				201	to the user initially for an <I>open</I> or <I>save</I> dialog, does
				202	<EM>not</EM> follow the Python working directory. Which folder is
				203	initially shown to the user is usually one of (a) the application
				204	folder, (b) the "Documents" folder or (c) the folder most recently
				205	used for such a dialog (in any Python program). This is standard MacOS
				206	behaviour, so don't blame Python for it. The exact behaviour is
				207	settable through a control panel since System 7.5.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	208
				209	<h2>Interactive startup file</h2>
				210
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	211	If the folder containing the interpreter contains a file named
				212	<CODE>PythonStartup</CODE> this file is executed when you start an
				213	interactive interpreter. In this file you could import modules you
				214	often use and other such things. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	215
				216
				217	<h2>Compiled python scripts</h2>
				218
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	219	Once a python module has been imported the interpreter creates a
				220	compiled version which is stored in a file with the ".py" extension
				221	replaced by ".pyc". These compiled files, with creator
				222	<CODE>'Pyth'</CODE> and type <CODE>'PYC '</CODE> load faster when
				223	imported (because they do not have to be parsed). The <CODE>Lib</CODE>
				224	folder contains a script <CODE>compileall.py</CODE>, running this
				225	script will cause all modules along the python search path to be
				226	precompiled, which will speed up your programs. Compiled files are
				227	also double-clickable. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	228
				229	<h2>Python resources</h2>
				230
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	231	MacPython has the ability to collect a number of compiled modules
				232	together in the resource fork of a single file. This feature is useful
				233	if you distribute a python program and want to minimize clutter: you
				234	can put all the needed modules in a single file (which could even be
				235	the interpreter itself). <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	236
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	237	If the module search path contains a filename as one of its entries
				238	(as opposed to a folder name, which is the normal case) this file will
				239	be searched for a resource with type <CODE>'PYC '</CODE> and a name
				240	matching the module being imported. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	241
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	242	The <CODE>scripts</CODE> folder contains a script
				243	<CODE>PackLibDir</CODE> which will convert a number of modules (or
				244	possibly a complete subtree full of modules) into such a resource
				245	file.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	246
				247	<h2><A NAME="preferences">Setting interpreter preferences</A></h2>
				248
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	249	The python interpreter keeps a preferences file in the standard
				250	location in the system folder. In this preferences file it remembers
				251	the default module search path and the default settings for the
				252	runtime options. The preferences are settable via
				253	<CODE>EditPythonPrefs</CODE>. For PPC python this is a standalone
				254	program living in the main Python folder, for 68K python it is a
				255	script in the <CODE>Scripts</CODE> folder. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	256
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	257	The interface to edit the preferences is rather clunky for the current
				258	release. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	259
				260	<img src="html.icons/preferences.gif"><p>
				261
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	262	In the editable text field at the top you enter the initial module
				263	search path, using newline as a separator. There are two special
				264	values you can use here: an initial substring <CODE>$(PYTHON)</CODE>
				265	will expand to the Python home folder and a value of
				266	<CODE>$(APPLICATION)</CODE> will expand to the the python application
				267	itself. Note that the text field may extend "beyond the bottom" even
				268	though it does not have a scroll bar. Using the arrow keys works,
				269	though.<p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	270
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	271	The Python home folder $(PYTHON) is initially, when you execute the
				272	interpreter for the first time, set to the folder where the
				273	interpreter lives. You can change it here. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	274
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	275	Finally, you can set the default startup options here, through a
				276	sub-dialog.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	277
				278	<h2>Applets</h2>
				279
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	280	An applet is a fullblown application written in Python, similar to an
				281	AppleScript applet (and completely different from a Java
				282	applet). Applets are currently only supported on PowerPC macintoshes,
				283	and are created using the <CODE>mkapplet</CODE> program. You create an
				284	applet by dropping the python source script onto mkapplet. The
				285	<CODE>Demo</CODE> folder contains an example of a more involved applet
				286	with its own resource file, etc. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	287
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	288	Note that while an applet behaves as a fullblown Macintosh application
				289	it is not self-sufficient, so distributing it to a machine without an
				290	installed Python interpreter will not work: it needs the shared python
				291	execution engine <CODE>PythonCore</CODE>, and probably various modules
				292	from the Lib and PlugIns folders. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	293
				294	<h2>Customizing applets</h2>
				295
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	296	Applets can have their own settings for the startup options and module
				297	search path. Dropping an applet on the <CODE>EditPythonPrefs</CODE>
				298	application allows you to set these, in the same way as
				299	double-clicking EditPythonPrefs allows you to set the system-wide
				300	defaults. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	301
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	302	Actually, not only applets but also the interpreter itself can have
				303	non-default settings for path and options. If you make a copy of the
				304	interpreter and drop this copy onto EditPythonPrefs you will have an
				305	interpreter that has a different set of default settings.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	306
				307	<h2>Where to go from here</h2>
				308
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	309	The previously mentioned <A
				310	HREF="http://www.python.org/doc/tut/tut.html">Python Tutorial</A> is
				311	an excellent place to start reading if you have never used Python
				312	before. Other documentation such as the library reference manual is
				313	indexed at the <A HREF="http://www.python.org/doc/">Python
				314	Documentation</A> page. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	315
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	316	There are some <A HREF="index.html">annotated sample programs</A>
				317	available that show some mac-specific issues, like use of various
				318	toolboxes and creation of Python applets. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	319
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	320	Finally, the <CODE>Demo</CODE> folder in the Macintosh distribution
				321	contains a number of other example programs. Most of these are only
				322	very lightly documented, but they may help you to understand some
				323	aspects of using Python. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	324
				325	The best way to contact fellow Macintosh Python programmers is to join
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	326	the MacPython Special Interest Group mailing list. Send a message with
				327	"info" in the body to <A
				328	HREF="mailto:pythonmac-sig-request@python.org">pythonmac-sig-request@python.org</A>
				329	or view the <A
				330	HREF="http://www.python.org/sigs/pythonmac-sig/">Pythonmac SIG
				331	page</A> on the <A HREF="http://www.python.org">www.python.org</A> WWW
				332	server. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	333
				334	<h2>Troubleshooting</h2>
				335
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	336	Python is a rather safe language, and hence it should be difficult to
				337	crash the interpreter of the system with a Python script. There is an
				338	exception to this rule, though: the modules that interface to the
				339	system toolboxes (windowing, quickdraw, etc) do very little error
				340	checking and therefore a misbehaving program using these modules may
				341	indeed crash the system. Such programs are unfortunately rather
				342	difficult to debug, since the crash does not generate the standard
				343	Python stack trace, obviously, and since debugging print statements
				344	will often interfere with the operation of the program. There is
				345	little to do about this currently. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	346
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	347	Probably the most common cause of problems with modules ported from
				348	other systems is the Mac end-of-line convention. Where unix uses
				349	linefeed, 0x0d, to separate lines the mac uses carriage return,
				350	0x0a. To complicate matters more a lot of mac programming editors like
				351	BBEdit and emacs will work happily with both conventions, so the file
				352	will appear to be correct in the editor but cause strange errors when
				353	imported. BBEdit has a popup menu which allows you to inspect (and
				354	set) the end-of-line convention used in a file. <p>
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	355
				356	<HR>
				357	<A HREF="http://www.cwi.nl/~jack">Jack Jansen</A>,
Jack Jansen	bd9565a	1996-04-15 12:25:44 +0000	[diff] [blame^]	358	<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 15-Apr-1996.
Jack Jansen	5f962c2	1996-04-10 14:52:59 +0000	[diff] [blame]	359
				360	</BODY>
				361	</HTML>