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- <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
- <html><head><title>Using the Open Scripting Architecture from Python</title></head>
- <body>
- <h1>Using the Open Scripting Architecture from Python</h1>
- <hr>
- <p><b>NOTE:</b> this document describes the OSA support that is shipped with
- the core python distribution. Most users are better of with the more
- userfriendly <a href="http://freespace.virgin.net/hamish.sanderson/appscript.html">appscript library</a>.
- <p>OSA support in Python is still not 100% complete, but
- there is already enough in place to allow you to do some nifty things
- with other programs from your python program. </p>
- <p>
- In this example, we will look at a scriptable application, extract its
- “AppleScript Dictionary,” generate a Python interface package from
- the dictionary, and use that package to control the application.
- The application we are going to script is Disk Copy, Apple's standard
- utility for making copies of floppies, creating files that are mountable
- as disk images, etc.
- Because we want
- to concentrate on the OSA details, we won’t bother with a real
- user-interface for our application. </p>
- <p>
- <em>When we say “AppleScript” in this document we actually mean
- “the Open Scripting Architecture.” There is nothing
- AppleScript-specific in the Python implementation. Most of this document
- focuses on the classic Mac OS; <a href="#osx">Mac OS X</a> users have some
- additional tools.</em>
- </p>
- <h2>Python OSA architecture</h2>
- <p>Open Scripting suites and inheritance can be modelled rather nicely
- with Python packages, so we generate
- a package for each application we want to script. Each suite defined in
- the application becomes a module in the
- package, and the package main module imports everything from all the
- submodules and glues together all the classes (in Python terminology—
- events in OSA terminology or verbs in AppleScript terminology). </p>
- <p>
- A suite in an OSA application can extend the functionality of a standard
- suite. This is implemented in Python by importing everything from the
- module that implements the standard suites and overriding anything that has
- been extended. The standard suites live in the StdSuite package. </p>
- <p>
- This all sounds complicated, but the good news is that basic
- scripting is actually pretty simple. You can do strange and wondrous things
- with OSA scripting once you fully understand it. </p>
- <h2>Creating the Python interface package</h2>
- <p>There is a tool in the standard distribution that can automatically
- generate the interface packages. This tool is called
- <code>gensuitemodule.py</code>, and lives in <code>Mac:scripts</code>.
- It looks through a file
- for an ‘AETE’ or ‘AEUT’ resource,
- the internal representation of the
- AppleScript dictionary, and parses the resource to generate the suite
- modules.
- When we start <code>gensuitemodule</code>, it asks us for an input file;
- for our example,
- we point it to the Disk Copy executable. </p>
- <p>
- Next, <code>gensuitemodule</code> wants a folder where it will store the
- package it is going to generate.
- Note that this is the package folder, not the parent folder, so we
- navigate to <code>Python:Mac:Demo:applescript</code>, create a folder
- <code>Disk_Copy</code>, and select that. </p>
- <p>
- We next specify the folder from which <code>gensuitemodule</code>
- should import the standard suites. Here,
- we always select <code>Python:Mac:Lib:lib-scriptpackages:StdSuites</code>. (There is
- one exception to this rule: when you are generating <code>StdSuites</code> itself
- you select <code>_builtinSuites</code>.)
- </p>
- <p>
- It starts parsing the AETE resource, and for
- each AppleEvent suite it finds, <code>gensuitemodule.py</code>
- prompts us for the filename of the
- resulting python module. Remember to change folders for the first
- module—you don't want to clutter up, say, the
- Disk Copy folder
- with your python
- interfaces. If you want to skip a suite, press <code>cancel</code> and the process
- continues with the next suite. </p>
- <h3>Summary</h3>
- <ol>
-
- <li>Run <code>gensuitemodule</code>.</li>
-
- <li>Select the application (or OSAX) for which you would like a Python interface.</li>
-
- <li>Select the package folder where the interface modules should be
- stored.</li>
-
- <li>Specify the folder <code>Python:Mac:Lib:lib-scriptpackages:StdSuites</code>
- to import the standard suites (or <code>_builtinSuites</code> if you are
- generating <code>StdSuites</code> itself). </li>
-
- <li>Save the generated suites (use <code>cancel</code> to skip a suite).</li>
-
-
- </ol>
- <h3>Notes</h3>
- <ul>
-
- <li>The interface package may occasionally need some editing by hand. For example,
- <code>gensuitemodule</code> does not handle all Python reserved words, so
- if
- one of the AppleScript verbs is a Python reserved word, a <code>SyntaxError</code>
- may be raised when the package is imported.
- Simply rename the class into something acceptable, if this happens;
- take a look at how the
- <code>print</code> verb is handled (automatically by <code>gensuitemodule</code>)
- in the standard suites. But: f you need to edit your package this should be considered a
- bug in gensuitemodule, so please report it so it can be fixed in future releases.
- </li>
-
-
- <li>If you want to re-create the StdSuite modules,
- you should look in one of two places. With versions of AppleScript older than 1.4.0
- (which first shipped with OS 9.0), you will find the
- AEUT resources in <code>System Folder:Extensions:Scripting
- Additions:Dialects:English Dialect</code>. For newer versions, you will
- find them in <code>System Folder:Extensions:Applescript</code>.
- </li>
- <li>Since MacPython 2.0, this new structure, with packages
- per application and submodules per suite, is used. Older MacPythons had a
- single level of modules, with uncertain semantics. With the new structure,
- it is possible for programs to override standard suites, as programs often do.
- </li>
- <li><code>Gensuitemodule.py</code> may ask you questions
- like “Where is enum 'xyz ' declared?”.
- This is either due to a misunderstanding on my part or (rather too commonly)
- bugs in the AETE resources. Pressing <code>cancel</code> is usually the
- right choice: it will cause the specific enum not to be treated as an enum
- but as a “normal” type. As things like fsspecs and TEXT strings clearly are
- not enumerators, this is correct. If someone understands what is really going on
- here, please let me know.</li>
- </ul>
- <h2>The Python interface package contents</h2>
- <p>
- Let’s glance at the
- <a href="applescript/Disk_Copy">Disk_Copy</a> package just created. You
- may want to open Script Editor alongside to see how it
- interprets the dictionary.
- </p>
- <p>
- The main package module is in <code>__init__.py</code>.
- The only interesting bit is the <code>Disk_Copy</code> class, which
- includes the event handling classes from the individual suites. It also
- inherits <code>aetools.TalkTo</code>, which is a base class that handles all
- details on how to start the program and talk to it, and a class variable
- <code>_signature</code> which is the default application this class will talk
- to (you can override this in various ways when you instantiate your class, see
- <code>aetools.py</code> for details).
- </p>
- <p>
- The <a href="applescript/Disk_Copy/Special_Events.py">Special_Events</a>
- module is a nice example of a suite module.
- The <code>Special_Events_Events</code> class is the bulk of the code
- generated. For each verb, it contains a method. Each method knows what
- arguments the verb expects, and it makes use of keyword
- arguments to present a palatable
- interface to the python programmer.
- Notice that each method
- calls some routines from <code>aetools</code>, an auxiliary module
- living in <code>Mac:Lib</code>.
- The other thing to notice is that each method calls
- <code>self.send</code>. This comes from the <code>aetools.TalkTo</code>
- baseclass. </p>
- <p>
- After the big class, there are a number of little class declarations. These
- declarations are for the (AppleEvent) classes and properties in the suite.
- They allow you to create object IDs, which can then be passed to the verbs.
- For instance,
- when scripting the popular email program Eudora,
- you would use <code>mailbox("inbox").message(1).sender</code>
- to get the name of the sender of the first message in mailbox
- inbox. It is
- also possible to specify this as <code>sender(message(1, mailbox("inbox")))</code>,
- which is sometimes needed because these classes don’t always inherit correctly
- from baseclasses, so you may have to use a class or property from another
- suite. </p>
- <p>
- Next we get the enumeration dictionaries, which allow you to pass
- english names as arguments to verbs, so you don't have to bother with the 4-letter
- type code. So, you can say
- <code>
- diskcopy.create(..., filesystem="Mac OS Standard")
- </code>
- as it is called in Script Editor, instead of the cryptic lowlevel
- <code>
- diskcopy.create(..., filesystem="Fhfs")
- </code></p>
- <p>
- Finally, we get the “table of contents” of the module, listing all
- classes and such
- by code, which is used by <code>gensuitemodule</code> itself: if you use this
- suite as a base package in a later run this is how it knows what is defined in this
- suite, and what the Python names are.
- </p>
- <h3>Notes</h3>
- <ul>
-
- <li>The <code>aetools</code> module contains some other nifty
- AppleEvent tools as well. Have a look at it sometime, there is (of
- course) no documentation yet.
- </li>
-
- <li>There are also some older object specifiers for standard objects in aetools.
- You use these in the form <code>aetools.Word(10,
- aetools.Document(1))</code>, where the corresponding AppleScript
- terminology would be <code>word 10 of the first
- document</code>. Examine
- <code>aetools</code> and <code>aetools.TalkTo</code>
- along with
- the comments at the end of your suite module if you need to create
- more than the standard object specifiers.
- </li>
-
- </ul>
- <h2>Using a Python suite module</h2>
- <p>
- Now that we have created the suite module, we can use it in a Python script.
- In older MacPython distributions this used to be a rather
- complicated affair, but with the package scheme and with the application signature
- known by the package it is very simple: you import the package and instantiate
- the class, e.g.
- <code>
- talker = Disk_Copy.Disk_Copy(start=1)
- </code>
- You will usually specify the <code>start=1</code>: it will run the application if it is
- not already running.
- You may want to omit it if you want to talk to the application
- only if it is already running, or if the application is something like the Finder.
- Another way to ensure that the application is running is to call <code>talker._start()</code>.
- </p>
- <p>
- Looking at the sourcefile <a
- href="applescript/makedisk.py">makedisk.py</a>, we see that it starts
- with some imports. Naturally, one of these is the Python interface to Disk
- Copy.</p>
- <p>
- The main program itself is a wonder of simplicity: we create the
- object (<code>talker</code>) that talks to Disk Copy,
- create a disk, and mount it. The bulk of
- the work is done by <code>talker</code> and the Python interface package we
- just created.</p>
- <p>
- The exception handling does warrant a few comments, though. Since
- AppleScript is basically a connectionless RPC protocol,
- nothing happens
- when we create the <code>talker</code> object. Hence, if the destination application
- is not running, we will not notice until we send our first
- command (avoid this as described above). There is another thing to note about errors returned by
- AppleScript calls: <code>MacOS.Error</code> is raised for
- all of the errors that are known to be <code>OSErr</code>-type errors,
- while
- server generated errors raise <code>aetools.Error</code>. </p>
- <h2>Scripting Additions</h2>
- <p>
- If you want to use any of the scripting additions (or OSAXen, in
- everyday speech) from a Python program, you can use the same method
- as for applications, i.e. run <code>gensuitemodule</code> on the
- OSAX (commonly found in <code>System Folder:Scripting Additions</code>
- or something similar). There is one minor gotcha: the application
- signature to use is <code>MACS</code>. You will need to edit the main class
- in the <code>__init__.py</code> file of the created package and change the value
- of <code>_signature</code> to <code>MACS</code>, or use a subclass to the
- same effect.
- </p>
- <p>
- There are two minor points to watch out for when using <code>gensuitemodule</code>
- on OSAXen: they appear all to define the class <code>System_Object_Suite</code>,
- and a lot of them have the command set in multiple dialects. You have to
- watch out for name conflicts and make sure you select a reasonable dialect
- (some of the non-English dialects cause <code>gensuitemodule</code> to generate incorrect
- Python code). </p>
- Despite these difficulties, OSAXen offer a lot of possibilities. Take a
- look at some of the OSAXen in the Scripting Additions folder, or
- <A HREF="http://www.osaxen.com/index.php">download</A> some from the net.
- <h2>Further Reading</h2>
- <p>
- If you want to look at more involved examples of applescripting, look at the standard
- modules <code>findertools</code> and <code>nsremote</code>, or (possibly better, as it
- is more involved) <code>fullbuild</code> from the <code>Mac:scripts</code> folder.
- </p>
- <h2><a name="alternatives">Alternatives</a></h2>
- <h3><a name="osx">Mac OS X</a></h3>
- <p>
- Under Mac OS X, the above still works, but with some new difficulties.
- The application package structure can hide the ‘AETE’ or
- ‘AEUT’ resource from <code>gensuitemodule</code>, so that,
- for example, it cannot generate an OSA interface to iTunes. Script
- Editor gets at the dictionary of such programs using a ‘Get
- AETE’ AppleEvent, if someone wants to donate code to use the same
- method for gensuitemodule: by all means!
- </p>
- <p>
- One alternative is available through the Unix command line version of python.
- Apple has provided the <code>osacompile</code> and <code>osascript</code> tools,
- which can be used to compile and execute scripts written in OSA languages. See the
- man pages for more details.
- </p>
- </body>
- </html>