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485 lines
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<HEAD>
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<TITLE>HOWTO: Compiling Python Modules with MPW</TITLE>
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</HEAD>
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<BODY>
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<H1>HOWTO: Compiling Python Modules with MPW</H1>
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<blockquote>
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This HOWTO is a slightly reformatted version of an original by
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<A HREF="mailto:cwebster@nevada.edu">Corran Webster</A>, whose
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<A HREF="http://www.nevada.edu/~cwebster/Python/">Python page</A>
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may contain a more up-to-date version.
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</blockquote>
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<HR>
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<P>
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The <A HREF="http://www.cwi.nl/~jack/macpython.html">Macintosh version</A>
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of the <A HREF="http://www.python.org/">Python programming language</A> is
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usually compiled with <A HREF="http://www.metrowerks.com/">Metrowerks
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CodeWarrior</A>. As a result, C extension modules are also usually
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compiled with CodeWarrior, and the documentation and sample code reflects
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this. CodeWarrior is a commercial product, and may be beyond the budgets
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of hobbyist hackers, making them dependent on others to compile C extension
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modules. At the present time, many standard C extension modules compile
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"out of the box" on the Macintosh, but in only a few cases is the plugin
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for the Macintosh included in the distribution.
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</P>
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<P>
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The <A HREF="http://developer.apple.com/tools/mpw-tools/">Macintosh
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Programmer's Workshop</A> (MPW) is Apple's development environment, and is
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freely available for <A
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HREF="ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/MPW_etc./">download</A>
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from Apple, as well as on their Developer CDs. Since Python was originally
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developed using MPW, before CodeWarrior became the dominant MacOS
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development environment, most of the idiosyncrasies of MPW are already
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supported, and compilation of C extension modules in MPW is possible.
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</P>
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<P>
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This HOWTO only deals with compiling for PowerPC Macintoshes. The process
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should be similar for 68k Macintoshes using the code fragment manager, but
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I have not attempted this - my old Mac is running NetBSD.
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</P>
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<P>
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This way of compiling modules is still experimental. Please read the
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caveats section below.
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</P>
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<H2><A NAME="setup">Setting Up MPW for Compiling Python Modules</A></H2>
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<P>
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This assumes that you have successfully installed both MPW and Python with
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the Developer's Kit on your Macintosh.
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</P>
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<P>
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The first step is to let MPW know where you keep Python. This step is not
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strictly necessary, but will make development easier and improve
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portability. Create a new file in the <CODE>Startup Items</CODE> folder of
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MPW called <A HREF="Python"><CODE>Python</CODE></A>. Type the lines:
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</P>
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<PRE>
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set Python "Macintosh HD:Applications:Python 1.5.2c1:"
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set PythonIncludes "{Python}Include"
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set PythonMacIncludes "{Python}Mac:Include"
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set PythonCore "{Python}PythonCore"
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export Python PythonIncludes PythonMacIncludes PythonCore
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</PRE>
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<P>
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where <CODE>Macintosh HD:Applications:Python 1.5.2c1:</CODE> is replaced by
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the path to the directory where you keep your copy of Python, and the other
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variables reflect where you keep your header files and Python core files.
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The locations here are the standard for Python 1.5.2c1, but they are
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different for Python 1.52b2 and earlier (most notably, the PythonCore is
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kept in the Extensions folder).
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</P>
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<P>
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Next, you need to update the <A HREF="config.h"><CODE>config.h</CODE></A>
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file for the <CODE>MrC</CODE> compiler included with MPW. This header file
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is located in the <CODE>:Mac:Include</CODE> folder in the standard
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distribution. You can update it by hand, by adding the lines:
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</P>
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<PRE>
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#ifdef __MRC__
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#define BAD_STATIC_FORWARD
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#endif
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</PRE>
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<P>
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at the after the similar defines for <CODE>__MWERKS__</CODE> and
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<CODE>__SC__</CODE> in the file. This step is critical: many modules,
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including ones in the standard distribution, will not compile properly
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without this modification (see common problems below).
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</P>
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<P>
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Copies of both the <A HREF="Python"><CODE>Python</CODE></A> startup item
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for MPW and the <A HREF="config.h"><CODE>config.h</CODE></A> are included
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here for your convenience.
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</P>
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<P>
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If you are porting Unix modules to the mac, you may find it useful to
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install <A
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HREF="http://www.iis.ee.ethz.ch/~neeri/macintosh/gusi-qa.html">GUSI</A> for
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your copy of MPW. GUSI provides some amount of POSIX compatibility, and is
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used by Python itself for this purpose - at the very least having it's
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header files available may be useful. Also of note for people porting Unix
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modules, the most recent alpha version (4.1a8) of <CODE>MrC</CODE> and
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<CODE>MrCpp</CODE> at this writing permits using unix-style pathnames for
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includes via the <CODE>-includes unix</CODE> command line option. I have
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not experimented heavily with this, but will be doing so in the future and
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report my findings.
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</P>
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<P>
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You now have MPW and Python set up to allow compilation of modules.
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</P>
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<H2><A NAME="compiling">Compiling a Module</A></H2>
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<P>
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This assumes that you have a C extension module ready to compile. For
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instructions on how to write a module, see the Python documentation.
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</P>
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<P>
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There are three approaches you can take to compiling in MPW: using the
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command line interface, using the MPW <CODE>CreateMake</CODE> command
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(available as the "Create build commands..." menu item, and writing a
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Makefile by hand.
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</P>
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<P>
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Before you start any of these, you'll need to know:
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</P>
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<UL>
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<LI>The names and locations of the C source files. In the examples, this
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is the file <A HREF="xxmodule.c"><CODE>xxmodule.c</CODE></A>, and is in
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MPW's current working directory.
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<LI>The name that Python expects to import your module under. In the
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examples, this is <CODE>xx</CODE>, so the shared library file will be
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called <CODE>xx.ppc.slb</CODE>.
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<LI>The location of any additional header files use by the C source. The
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example does not use any additional header files.
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<LI>The location of any additional shared libraries which the module needs
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to link to. The example does not link to any other shared libraries.
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<LI>The name of the entry point to your module. This is usually the last
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function in the main C source file, and the name usually starts with
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<CODE>init</CODE>. In the examples, this is <CODE>initxx</CODE>.
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</UL>
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<H3>Using the Command Line</H3>
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<P>
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For simple modules consisting of one or two C files, it's often convenient
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to simply use commands in a MPW Worksheet. Usually you will want to set
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MPW's working directory to the directory containing the C source code. The
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following commands compile and link the standard Python test module <A
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HREF="xxmodule.c"><CODE>xxmodule.c</CODE></A>:
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</P>
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<PRE>
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MrC "xxmodule.c" -o "xx.c.x" -w off -d HAVE_CONFIG_H ∂
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-i "{PythonMacIncludes}" ∂
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-i "{PythonIncludes}"
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PPCLink ∂
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-o "xx.ppc.slb" ∂
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"xx.c.x" ∂
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-t 'shlb' ∂
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-c 'Pyth' ∂
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-xm s ∂
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-d ∂
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"{PythonCore}" ∂
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"{SharedLibraries}InterfaceLib" ∂
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"{SharedLibraries}MathLib" ∂
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"{SharedLibraries}StdCLib" ∂
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"{PPCLibraries}StdCRuntime.o" ∂
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"{PPCLibraries}PPCCRuntime.o" ∂
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"{PPCLibraries}PPCToolLibs.o" ∂
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-export initxx
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</PRE>
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<P>
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(Note: The last character on each line should appear as "partial
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derivative" symbol, which you type as <KBD>option-d</KBD> and which is
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MPW's line continuation symbol.)
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</P>
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<P>
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Any additional header files should be specified by adding their directories
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as extra <CODE>-i</CODE> options to the <CODE>MrC</CODE> command. Any
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additional shared libraries should be added before the PythonCore library
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in the <CODE>PPCLink</CODE> command.
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</P>
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<P>
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If there is more than one source file, you will need to duplicate the
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compile command for each source file, and you will need to include all the
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object files in the place where <CODE>"xx.c.x"</CODE> appears in the
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<CODE>PPCLink</CODE> command.
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</P>
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<H3>Using CreateMake</H3>
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<P>
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For more complex modules, or modules that you are writing yourself, you
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will probably want to use a makefile. Unfortunately MPW's makefiles are
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incompatible with the standard Unix makefiles, so you will not be able to
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use any makefiles which come with a C module.
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</P>
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<P>
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Usually, you will want the makefile to reside in the same directory as the
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C source code, so you should set MPW's working directory to that directory
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before proceeding.
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</P>
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<P>
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To create a makefile for the standard Python test module <A
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HREF="xxmodule.c"><CODE>xxmodule.c</CODE></A>:
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</P>
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<UL>
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<LI>Select "Create build commands..." from the "Build" Menu.
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<LI>Type <KBD>xx.ppc.slb</KBD> for the Program Name.
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<LI>Select "Shared Library" for the Program Type.
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<LI>Select "PowerPC Only" for the Target.
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<LI>Click on the "Source Files..." button, and add your module's C source
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files to the list.
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<LI>Click on the "Other Options..." button and change the creator type to
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"Pyth". If you are using additional header files, you can also add their
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directories at this stage. Click on "Continue" once you have done this.
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<LI>Click on the "Exported Symbols..." button and type <KBD>initxx</KBD>
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into the entry field. Click on "Continue" once you have done this.
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<LI>At this stage, your CreateMake window should look like this: <IMG
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SRC="html.icons/createmake.png" ALT="[picture of commando window for CreateMake]">
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<LI>Click on the "CreateMake" button.
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</UL>
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<P>
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You will now need to edit the makefile that was just created. Open the
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file "xx.ppc.slb.make" in the current directory and make the following
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changes:
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</P>
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<UL>
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<LI>Change the line
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<PRE>
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Includes =
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</PRE>
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<P>
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to read
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</P>
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<PRE>
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Includes = -i "{PythonIncludes}" -i "{PythonMacIncludes}"
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</PRE>
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<P>
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If you have any additional headers than need to be included, you can add
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them here as well.
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<LI>Change the line
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<PRE>
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PPCCOptions = {Includes} {Sym•PPC}
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</PRE>
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<P>
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to read
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</P>
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<PRE>
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PPCCOptions = -w off -d HAVE_CONFIG_H {Includes} {Sym•PPC}
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</PRE>
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<P>
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<LI>After the line
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<PRE>
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-xm s ∂
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</PRE>
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<P>
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add
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</P>
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<PRE>
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-d ∂
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"{PythonCore}" ∂
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</PRE>
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<P>
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If you have any other shared libraries you need to link to, add each on a
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line before PythonCore, terminating each line with a <CODE>∂</CODE>.
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</P>
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</UL>
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<P>Save the file. You are now ready to build.
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</P>
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<P>
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Go to the "Build" or "Full Build" menu items, type in
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<KBD>xx.ppc.slb</KBD>, and MPW should take things from there. Any time you
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need to rebuild the shared library, you can simply do another "Build" or
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"Full Build".
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</P>
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<H3>Writing a Makefile by Hand</H3>
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<P>
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For modules which have complex interdependencies between files, you will
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likely need a more sophisticated makefile than the one created by
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<CODE>CreateMake</CODE>. You will need to be familiar with the MPW
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makefile format, but you can get a start by either using
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<CODE>CreateMake</CODE> to get a simple starting point, or taking another
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MPW makefile as a starting point.
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</P>
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<P>
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It is beyond the scope of this HOWTO to go into the generalities of MPW
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makefiles. Documentation on MPW's <CODE>Make</CODE> command can be found
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with the MPW distribution, in particular the documents <A
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HREF="http://developer.apple.com/tools/mpw-tools/books.html#Building">Building
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and Maintaining Programs with MPW (2nd Edition)</A> and the <A
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HREF="http://developer.apple.com/tools/mpw-tools/books.html#CommandRef">MPW
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Command Reference</A>.
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</P>
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<P>
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There are a couple of important points to keep in mind when writing a
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makefile by hand:</P>
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<UL>
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<LI>When there are multiple symbols with the same name in object files or
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shared libraries, <CODE>PPCLink</CODE> used the symbol from the file which
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appears first in arguments of the <CODE>PPCLink</CODE> command. For this
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reason, you will usually want the PythonCore and any other shared libraries
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which are not part of the standard MPW runtime environment to appear before
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the standard runtime libraries. This is particularly the case with
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StdCLib. The "-d" option turns off the (often copious) warnings about
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multiply defined symbols.
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<LI>You will want to make sure that the <CODE>HAVE_CONFIG_H</CODE>
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preprocessor symbol is defined for most C source files using the <CODE>-d
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HAVE_CONFIG_H</CODE> option to <CODE>MrC</CODE>.
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</UL>
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<P>
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The file <A HREF="xx.ppc.slb.make.sit.hqx"><CODE>xx.ppc.slb.make</CODE></A>
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is included here for you to use as a starting point.
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</P>
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<H2><A NAME="using">Using the Extension Module</A></H2>
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<P>
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Once you have compiled your extension module, you will need to let Python
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know where it is. You can either move it into a place on Python's search
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path - such as the <CODE>:Mac:Plugins</CODE> folder - or modify the path to
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include the location of your new module using the
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<CODE>EditPythonPrefs</CODE> applet.
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</P>
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<P>
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Your work may not be completely done, as many extension modules have a
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Python wrapper around them. If the Python was not written with portability
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in mind, you may need to do some more work to get that up and running.
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Indeed, if the Python part uses OS-specific features, like pipes, you may
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have to completely rewrite it if you can make it work at all.
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</P>
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<H2><A NAME="problems">Common Problems</A></H2>
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<P>
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There are a couple of common problems which occur when porting a module
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from another platform. Fortunately, they are often easy to fix.
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</P>
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<H3>Static Forward Definitions</H3>
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<P>
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If you get a compiler error which looks something like:
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</P>
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<PRE>
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File "xxmodule.c"; line 135 #Error: 'Xxo_Type' is already defined
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</PRE>
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<P>
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then most likely either you have not set up <CODE>config.h</CODE> correctly
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to handle static forward definitions, or the module author has not adhered
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to the standard python conventions. If the second is the case, find where
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the variable is first defined, and replace the <CODE>static</CODE> with
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<CODE>staticforward</CODE>. Then find the second place it is defined
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(usually the line where the compiler complained) and replace
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<CODE>static</CODE> with <CODE>statichere</CODE>.
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</P>
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<P>
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If you have set up things correctly, you should now be able to compile.
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</P>
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<H3>Automatic Type Conversion</H3>
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<P>
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<CODE>MrC</CODE> seems to be a little pickier about automatically
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converting from one type to another than some other C compilers. These can
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often be fixed by simply adding an explicit cast to the desired type.
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</P>
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<P>
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XXX There may be a compiler option which relaxes this. That would be a
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better solution.
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</P>
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<H2><A NAME="caveats">Caveats</A></H2>
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<P>
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As Jack Jansen pointed out on the Mac Python mailing list, there could
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potentially be conflicts between the MetroWerks C runtime which the Python
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core and standard modules was compiled with, and the MPW C runtime which
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your extension module is compiled with. While things seem to work fine in
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everyday use, it is possible that there are bugs which have not been
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discovered yet. Most likely these world take the form of standard C
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functions (most likely I/O functions due to conflicts between the SIOUX
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libraries and the SIOW libraries) not working as they are supposed to, or
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memory leaks caused by improper malloc/free.
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</P>
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<P>
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Some such problems have been demonstrated by compiling modules with
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PythonCore linked after StdCLib - printf does not work properly in this
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setup, and I suspect that there will also be malloc/free problems in
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situations where the module allocates memory which is later disposed of by
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Python, or vice-versa. Compiling with PythonCore taking precedence over
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StdCLib seems to give the correct behaviour.
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</P>
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<P>
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This method of compiling should be considered experimental for the time
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being. <STRONG>Use it at your own risk.</STRONG>
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</P>
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<P>
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If you notice any quirks in modules compiled this way, or have insight into
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what may go wrong or right with this situation, <A
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HREF="mailto:cwebster@nevada.edu">please contact me</A> so that I can add
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it to the HOWTO.
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</P>
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<P>
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The ideal solution to this problem would be to get Python to compile using
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MPW (and a Python MPW Tool would be very neat indeed). However, that does
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seem to be a major project.
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</P>
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<DIV class=footer>
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<HR>
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<BR>
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©<A HREF="mailto:cwebster@nevada.edu">Corran Webster</A>, 1999. <BR>
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<!-- #LASTMODIFIED TEXT="Last modified" FORM="SHORT,TIME" -->
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Last modified 14/12/99 12:17 PM
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