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| author | Jack Jansen <jack.jansen@cwi.nl> | 1996-04-10 14:52:59 (GMT) |
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| committer | Jack Jansen <jack.jansen@cwi.nl> | 1996-04-10 14:52:59 (GMT) |
| commit | 5f962c2a75a09bd9e35f32c0250abcfd8c738154 (patch) | |
| tree | 9d1399c806284b5b6af5f720b0dae9cf02d1c1bd /Mac/Demo/using.html | |
| parent | 822a30b0eea58028eca93b34d7674fc511bbdbce (diff) | |
| download | cpython-5f962c2a75a09bd9e35f32c0250abcfd8c738154.zip cpython-5f962c2a75a09bd9e35f32c0250abcfd8c738154.tar.gz cpython-5f962c2a75a09bd9e35f32c0250abcfd8c738154.tar.bz2 | |
Added a tutorial
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| -rw-r--r-- | Mac/Demo/using.html | 279 |
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diff --git a/Mac/Demo/using.html b/Mac/Demo/using.html new file mode 100644 index 0000000..872bb9e --- /dev/null +++ b/Mac/Demo/using.html @@ -0,0 +1,279 @@ +<HTML> +<HEAD> +<TITLE>Using Python on the Macintosh</TITLE> +</HEAD> +<BODY> +<H1>Using Python on the Macintosh</H1> +<EM>(preliminary)</EM> +<HR> + +This document is an introduction to using Python on the Apple Macintosh. +It does not introduce the language itself, for this you should refer +to the <A HREF="http://www.python.org/doc/tut/tut.html">Python Tutorial</A> +by Guido van Rossum. This guide +more-or-less replaces chapter two of the tutorial, and provides some +additional material. <p> + +The document refers to Python 1.3.3 or higher, some of the features (like +setting applet options) will not work in earlier versions of Python. <p> + +<h2>Invoking the interpreter</h2> + +The name of the interpreter may differ on different installations: it may +be called <CODE>Python</CODE>, <CODE>PythonPPC</CODE> (for powerpc macs) or +<CODE>Python68K</CODE> (indeed, for 68K macs). It will always be recognizable by +the "16 ton" icon, though. You start the interpreter in interactive mode by +double-clicking it. <p> + +<img src="html.icons/python.gif"><p> + +This should give you a text window with an informative version string and a prompt, +something like the following: +<PRE> +Python 1.3.3 (Apr 7 1996) [CW PPC w/GUSI] +Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam +>>> +</PRE> +The version string tells you the version of Python, whether it was built for +PPC or 68K macs and possibly some options used to build the interpreter. If +you find a bug or have a question about how the interpreter works it is a good +idea to include the version information in your message. <p> + +At the prompt you can type interactive python commands. See the tutorial for +more information. The interactive window works more-or-less like a Communication +Toolbox or Telnet window: you type commands at the bottom and terminate them with +the <EM>[return]</EM> or <EM>[enter]</EM> key. Interpreter feedback also appears +at the bottom of the window, and the contents scroll as output is added. You can +use copy and paste in the normal way, but be sure to paste only at the bottom +of the document. + +<h2>Creating Python scripts</h2> + +The Python interpreter works in a way that is different from what you would +expect of a macintosh program: the interpreter is just that: an interpreter. +There is no builtin editor or other development support. Hence, to create +a Python script you need an external text editor. For a first script you +can use any editor that can create plain, unstyled text files, such as +<CODE>SimpleText</CODE>. <p> + +For more serious scripts, though, it is advisable to use a programmers editor, +such as <CODE>BBEdit</CODE> or <CODE>Alpha</CODE>. BBEdit is my favorite: it comes in a +commercial version but also in a fully-functional free version +<CODE>BBEdit Lite</CODE>. You can download it from the +<A HREF="http://www.barebones.com/">BareBones</A> site. +The free version will probably provide all the functionality you will ever need. +Besides the standard edit facilities it has multi-file searches and many other +goodies that can be very handy when editing programs. <p> + +After you have created your script in the editor of your choice you drop it on +the interpreter. This will start the interpreter executing the script, again with +a console window in which the output appears and in which you can type input if +the script requires it. Normally the interpreter will close the window and quit +as soon as the script is done executing, see below under +<A HREF="#startup">startup options</A> +for a way to change this. <p> + +It is a good idea to have the names of all your scripts end in <CODE>.py</CODE>. While +this is not necessary for standalone scripts it is needed for modules, and it is +probably a good idea to start the habit now. <p> + +<h2>Clickable python scripts</h2> + +If you create your script with the correct creator and type, creator <CODE>'Pyth'</CODE> +and type <CODE>'TEXT'</CODE>, you can double-click your script and it will automatically +invoke the interpreter. If you use BBEdit you can tell it about the Python file +type by adding it to the "file types" sections of the preferences. Then, if you save +a file for the first time you can tell BBEdit to save the file as a Python script +through the "options" choice of the save dialog. <p> + +The <CODE>Scripts</CODE> folder contains a script <CODE>fixfiletypes</CODE> that will +recursively traverse a folder and set the correct creator and type for all files +ending in <CODE>.py</CODE>. <p> + +<h2>Interaction with the user</h2> + +Normally, the interpreter will check for user input (mouse clicks, keyboard +input) every once in a while, so it is possible to switch to other applications +while a script runs. It is also possible to interrupt the interpreter with +the standard command-period keypress, this will raise the <CODE>KeyboardInterrupt</CODE> +exception. Scripts may, however, turn off this behaviour to facilitate their +own event handling. Such scripts can only be killed with the command-option-escape +shortcut. + +<h2><A NAME="startup">startup options</A></h2> + +If the <EM>option</EM> key is depressed when Python starts executing the +interpreter will bring up an options dialog thru which you can influence the way +the interpreter behaves. Keep the option key depressed until the dialog comes up. <p> + +<img src="html.icons/options.gif"><p> + +The options modify the interpreters behaviour in the following way: +<ul> +<li> the interpreter goes to interactive mode (in stead of +exiting) after a script has terminated normally, +<li> for every module imported a line is printed telling you where the +module was loaded from, +<li> do not print the values of expressions executed as statements in an +interactive python, +<li> do not buffer stdout and stderr, +<li> print some debugging output during the parsing phase, +<li> keep the output window open when a script terminates. +</ul> +In addition, you can enter a unix-style command line which is passed to the script +in <CODE>sys.argv</CODE>. Sys.argv[0] is always the name of the script being executed, +additional values can be passed here. Quoting works as expected. <p> + +The default options are also settable on a system-wide basis, see the section on +<A HREF="#preferences">editing preferences</A>. <p> + +<h2>Module search path</h2> + +The module search path, <CODE>sys.path</CODE>, contains the folders python will search +when you import a module. The path is settable on a system-wide basis (see the +preferences section), and normally comprises the current folder (where the script +lives), the <CODE>Lib</CODE> folder and some of its subfolders and possibly some more. <p> + +<h2>Working folder</h2> + +The unix concept of a <I>working directory</I> does not translate directly to +a similar concept on the Macintosh. To facilitate easy porting and the use of +relative pathnames in scripts the interpreter simulates a working directory. When +a script is started the initial working directory is the folder where the script +lives. In case of an interactive interpreter the working directory is the folder +where the interpreter lives. The "standard file" folder does <EM>not</EM> follow +the working directory, it follows the standard MacOS rules (which are settable +through a control panel since MacOS 7.5). + +<h2>Interactive startup file</h2> + +If the folder containing the interpreter contains a file named <CODE>PythonStartup</CODE> +this file is executed when you start an interactive interpreter. In this file you +could import modules you often use and other such things. <p> + + +<h2>Compiled python scripts</h2> + +Once a python module has been imported the interpreter creates a compiled version +which is stored in a file with the ".py" extension replaced by ".pyc". These +compiled files, with creator <CODE>'Pyth'</CODE> and type <CODE>'PYC '</CODE> load faster +when imported (because they do not have to be parsed). The <CODE>Lib</CODE> folder +contains a script <CODE>compileall.py</CODE>, running this script will cause all modules +along the python search path to be precompiled, which will speed up your programs. +Compiled files are also double-clickable. <p> + +<h2>Python resources</h2> + +MacPython has the ability to collect a number of compiled modules together +in the resource fork of a single file. This feature is useful if you +distribute a python program and want to minimize clutter: you can put all the +needed modules in a single file (which could even be the interpreter itself). <p> + +If the module search path contains a filename as one of its entries (as opposed to +a folder name, which is the normal case) this file will be searched for a resource +with type <CODE>'PYC '</CODE> and a name matching the module being imported. <p> + +The <CODE>scripts</CODE> folder contains a script <CODE>PackLibDir</CODE> which will convert +a number of modules (or possibly a complete subtree full of modules) into such a +resource file. + +<h2><A NAME="preferences">Setting interpreter preferences</A></h2> + +The python interpreter keeps a preferences file in the standard location in the +system folder. In this preferences file it remembers the default module search +path and the default settings for the runtime options. The preferences are settable +via <CODE>EditPythonPrefs</CODE>. For PPC python this is a standalone program living +in the main Python folder, for 68K python it is a script in the <CODE>Scripts</CODE> +folder. <p> + +The interface to edit the preferences is rather clunky for the current release. <p> + +<img src="html.icons/preferences.gif"><p> + +In the editable text field at the top you enter the initial module search path, +using newline as a separator. There are two special values you can use here: +an initial substring <CODE>$(PYTHON)</CODE> will expand to the Python home folder +and a value of <CODE>$(APPLICATION)</CODE> will expand to the the python application +itself. Note that the text field may extend "beyond the bottom" even though it +does not have a scroll bar. Using the arrow keys works, though.<p> + +The Python home folder $(PYTHON) is initially, when you execute the interpreter +for the first time, set to the folder where the interpreter lives. You can change it +here. <p> + +Finally, you can set the default startup options here, through a sub-dialog. + +<h2>Applets</h2> + +An applet is a fullblown application written in Python, similar to an AppleScript +applet (and completely different from a Java applet). Applets are currently only +supported on PowerPC macintoshes, and are created using the <CODE>mkapplet</CODE> +program. You create an applet by dropping the python source script onto mkapplet. +The <CODE>Demo</CODE> folder contains an example of a more involved applet with its +own resource file, etc. <p> + +Note that while an applet behaves as a fullblown Macintosh application it is +not self-sufficient, so distributing it to a machine without an installed Python +interpreter will not work: it needs the shared python execution engine +<CODE>PythonCore</CODE>, and probably various modules from the Lib and PlugIns folders. <p> + +<h2>Customizing applets</h2> + +Applets can have their own settings for the startup options and module search +path. Dropping an applet on the <CODE>EditPythonPrefs</CODE> +application allows you to set +these, in the same way as double-clicking EditPythonPrefs allows you to set +the system-wide defaults. <p> + +Actually, not only applets but also the interpreter itself can have non-default +settings for path and options. If you make a copy of the interpreter and drop +this copy onto EditPythonPrefs you will have an interpreter that has a different +set of default settings. + +<h2>Where to go from here</h2> + +The previously mentioned <A HREF="http://www.python.org/doc/tut/tut.html">Python +Tutorial</A> is an excellent place to start reading if you have never used +Python before. Other documentation such as the library reference manual is +indexed at the <A HREF="http://www.python.org/doc/">Python Documentation</A> +page. <p> + +There are some <A HREF="index.html">annotated sample programs</A> available +that show some mac-specific issues, like use of various toolboxes and creation +of Python applets. <p> + +Finally, the <CODE>Demo</CODE> folder in the Macintosh distribution contains +a number of other example programs. Most of these are only very lightly documented, +but they may help you to understand some aspects of using Python. <p> + +The best way to contact fellow Macintosh Python programmers is to join +the MacPython Special Interest Group mailing list. Send a message with "info" +in the body to <A HREF="mailto:pythonmac-sig-request@python.org">pythonmac-sig-request@python.org</A> +or view the <A HREF="http://www.python.org/sigs/pythonmac-sig/">Pythonmac SIG page</A> on the +<A HREF="http://www.python.org">www.python.org</A> WWW server. <p> + +<h2>Troubleshooting</h2> + +Python is a rather safe language, and hence it should be difficult to crash the +interpreter of the system with a Python script. There is an exception to this rule, +though: the modules that interface to the system toolboxes (windowing, quickdraw, +etc) do very little error checking and therefore a misbehaving program using these +modules may indeed crash the system. Such programs are unfortunately rather +difficult to debug, since the crash does not generate the standard Python stack +trace, obviously, and since debugging print statements will often interfere with +the operation of the program. There is little to do about this currently. <p> + +Probably the most common cause of problems with modules ported from other +systems is the Mac end-of-line convention. Where unix uses linefeed, 0x0d, to +separate lines the mac uses carriage return, 0x0a. To complicate matters more +a lot of mac programming editors like BBEdit and emacs will work happily with +both conventions, so the file will appear to be correct in the editor but cause +strange errors when imported. BBEdit has a popup menu which allows you to inspect +(and set) the end-of-line convention used in a file. <p> + +<HR> +<A HREF="http://www.cwi.nl/~jack">Jack Jansen</A>, +<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 7-Apr-1996. + +</BODY> +</HTML> |