Re: Boost.Python support for Py 2.1 rich comparisons

From: nksauter_at_[hidden]
Date: 2001-05-22 02:58:15

As a follow up to my previous posting, I have implemented
Boost.Python support for Python 2.1 rich comparisons.  
Initially I was only able to customize the comparison methods 
(__lt__, __le__, etc.), but subsequently I overloaded the Python 
operators themselves, so that a < b will give a result of 
any desired type, rather than an integer 0 or 1.  

The key to doing this is that a pointer to a user-defined rich 
comparison function must be registered in the PyTypeObject of the 
extension class; also a bit flag must be set indicating that rich 
comparisons are available.  Thus the following lines of code are
added to Boost.Python types.cpp:
  dest->tp_richcompare = &do_instance_richcompare;
  dest->tp_flags |= Py_TPFLAGS_HAVE_RICHCOMPARE;
I also added appropriate guards so that Boost.Python is still 
backwards compatible with earlier Python versions.

I'm placing an overlay tarball with my source code and test case 
on my web page at http://cci.lbl.gov/sauter/richcmp_overlay.tar.gz, 
along with a makefile at http://cci.lbl.gov/sauter/makefile.  The 
overlay is meant to be used in conjunction with boost_1_21_2.  I've 
tested this on Compaq alpha/cxx, Linux/gcc, and Irix/CC; with Python 
2.1 and Python 1.5.2.  

Hopefully we can see something like this incorporated into a future 
Boost release.

Cheers,
Nick Sauter, LBNL