> Why did you want to customize "is"?
Well, mostly out of principle ;-)
But also because I'm wrapping a C library which passes around C structs
which are wrapped in shim C++ classes for a Boost.Python layer. Boost
Python does a marvelous job of translating between Python and C++ data
types; when a C structure is returned, it magically translates that
structure into a Python wrapper. The problem is that a _new_ Python
wrapper is created every time a pointer is returned, even if a wrapper
already exists for that particular pointer.
To illustrate: Suppose you have a function in C++ which is a simple
identity function, e.g.
template <typename T>
T *identity (T *x) {
return x;
}
Calling the wrapped version of this function from Python will produce a
Python wrapper which represents the same underlying C++ object, but is
not actually the same Python object:
>>> b = identity(a)
>>> b is a
False
I wanted to override the behavior of "is" so that (a is b) would be
True --- which shouldn't have caused a problem, since the wrapper
class's attributes are read-only from Python. As it is, I've overriden
__cmp__ and __hash__, so at least I get the correct dictionary behavior
>>> mydict = { a : 'something' }
>>> b = identity(a)
>>> b in mydict
True
It's quite possible that there is some way to do this correctly from
the Boost.Python side of things... my understanding of how to use
Boost.Python is minimal.
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