cpython/Tools/bgen

BGEN -- An Experiment: Automatic Generation of Extension Modules
================================================================

This directory contains BGEN -- a package that helps in generating
complete source code for Python extension module.  It currently also
contains a set of examples that were generated with BGEN.  These
examples are mostly interfaces to a number of important managers in
the Macintosh toolbox.


Overview of Subdirectories
--------------------------

Main subdirectories:

bgen	the code generator package

Example subdirectories:

ae	AppleEvents
ctl	Controls
dlg	Dialogs
evt	Events
menu	Menus
list	Lists
qd	QuickDraw
res	Resources
snd	Sound
win	Windows


Contents of Subdirectories
--------------------------

The contents of each example subdirectory is similar (<Foobar> is
for instance AppleEvents, while <foo> is ae):

<foo>scan.py	Scan the <Foobar>.h header, generating <foo>gen.py
<foo>gen.py	Output of <foo>scan.py, input for <foo>support.py
<foo>edit.py	Manually written complement of <foo>gen.py, sometimes
<foo>support.py	Generate <Foo>module.c from <foo>gen.py and <foo>edit.py
<Foo>module.c	The interface module, ready to be compiled
<Foobar>.py	Symbolic constants extracted from <Foobar.h>


Tests and Examples
------------------

Other files in these subdirectories are usually examples using the
extension.  If there's a file t<foo>.py, it usually is a really
boring test program.

Some test programs contain pathnames that should be edited before
trying them.

Some of the less boring tests and examples:

At the top level:

test.py		Application mainloop, uses most Mac extensions

In ae:

aetools.py	Conversions between AE and Python data type
echo.py		Dummy AE server, echoes all data back
tell.py		Primitive AE client
aete.py		Decode 'aete' and 'aeut' resources (incomplete)
gensuitemodule.py
		Read aete/aeut resources and turn them into python
		modules. The *_Suite.py modules have been generated
		with this.
AEservertest.py	A simple AE server, similar to echo but different.
		

In res:

listres.py	List *all* resources in current and in all res files
copyres.py	Copy a resource file
mkerrstrres.py	Read "errors.txt" and create a set of "Estr" resources

In snd:

playaiff.py	Play an AIFF file
morse.py	Turn text into Morse code
audiodev.py	The standard audiodev.py extended with Mac support
Audio_mac.py	The Mac support for audiodev.py


Creating new Macintosh interfaces
---------------------------------

These instructions were written up by Jack while he was building the
interface to Lists.h, the macintosh list manager. they may or may not
have a more global scope than exactly that.

First, start by copying ...scan.py and ...support.py from another,
preferrably similar type. I started with evt, but that was a mistake
since evt has no "own" object. Ctl or Dlg would probably have been a
better idea.

Now, the first thing to do is to comment out the blacklisted types and
functions and the transformation rules for arguments, we'll fill those
in lateron. Also, change the various definitions at the top, so that
the right include file is parsed, and the .py files are generated with
the correct name. If your manager has a type that will be implemented
as a python object you may as well now change the destination() method
to recognize that. (List was funny in this respect, since it has the
list as the last argument in stead of the first).

Now run your scanner. This will probably go fine until it tries to
execute the generated code in the ...gen.py module. Look at that file,
it will have formalized "definitions" of all the functions and methods
that will be generated. Look at them all (with the documentation of the
manager you're implementing in hand). Now you'll have to fix the
blacklists and the repair instructions. This is sort of a black art,
but a few guidelines may be handy here: 
- If there are argument types you cannot implement (or want to leave for
  the moment) put them in blacklisttypes. Complex structures come to
  mind, or routine pointers/UPP's. You will probably also want to
  blacklist the routine that disposes of your object (since you'll do
  that in the python destruction routine).
- Various types of buffers are available in bgenBuffer, bgenHeapBuffer
  and macsupport in the bgen directory. These'll let you handle all
  sorts of input and output parameters. You can put instructions in the
  repair list to let the C-arguments be handled by the correct type
  of buffer. Check the other bgen-generated modules for using this for
  passing raw structures and input and output buffers.
- It appears that the parser usually guesses correctly whether a parameter
  is meant for input or output. But, check the routines to be sure.
- Some types are pretty hard to handle but you need the functionality
  the a routine that uses them anyway. Various routines expecting ProcPtrs
  or RegionHandles come to mind. Often, you can use the FakeType class
  to provide a sensible default (i.e. NULL or a pointer to a routine you
  coded in C, or a region specifying "the whole window"). This way, python
  programmers won't get the full functionality but at least they'll get the
  common case. You put the FakeType stuff in ...support.py.
  
Next you'll probably have to write the code to implement your object.
This will probably be a subclass of GlobalObjectDefinition. This goes
into ...support.py. Also, some types used by the manager may look
enough like standard types that you can equate them here (there are a
lot of 2-integer structures that look remarkably like a Point, for
instance).

You'll also have to define the Function() and Method() classes. The
OSErrFunctionGenerator and its method-counterpart are particularly
handy for a lot of mac managers.

Finally, you'll have to try and compile your resulting C-source, and go
through the steps above until it works. For tlist.py, the test program
for list, I started with the application framework. This is probably a
good idea for any manager that does something to the display, since
ApplicationFramework takes care of all the intricacies of event
handling and decoding (up to a point).