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Adding a Py_EnterRecursiveCall() in PyObject_Call() seems to fix all the examples so far, with the exception of the "__get__=getattr" one, where we get a strange result instead of a RuntimeError (I suspect careless exception eating is taking place).

The main loop in ceval.c doesn't call PyObject_Call() very often: it usually dispatches directly itself for performance, which is exactly what we want here, as recursion from ceval.c is already protected by a Py_EnterRecursiveCall().  So this change has a minor impact on performance.  Pystone for example issues only three PyObject_Call() per loop, to call classes.  This has an almost-unmeasurable impact ( < 0.4%).

Of course I'll think a bit more and search for examples that don't go through PyObject_Call()  :-)