- Use the compare nesting level and in-progress dictionary properly in
PyObject_RichCompare().
- Change the in-progress code to use static variables instead of
globals (both the nesting level and the key for the thread dict were
globals but have no reason to be globals; the key can even be a
function-static variable in get_inprogress_dict()).
- Rewrote try_rich_to_3way_compare() to benefit from the similarity of
the three cases, making it table-driven.
- In try_rich_to_3way_compare(), test for EQ before LT and GT. This
turns out essential when comparing recursive UserList instances;
with the old code, these would recurse into rich comparison three
times for each nesting level up to NESTING_LIMIT/2, making the total
number of calls in the order of 3**(NESTING_LIMIT/2)!
NOTE: I'm not 100% comfortable with this. It works for the standard
test suite (which compares a few trivial recursive data structures
only), but I'm not sure that the in-progress dictionary is used
properly by the rich comparison code. Jeremy suggested that maybe the
operation should be included in the dict. Currently I presume that
objects in the dict are equal unless proven otherwise, and I set the
outcome for the rich comparison accordingly: true for operators EQ,
LE, GE, and false for the other three. But Jeremy seems to think that
there may be counter-examples where this doesn't do the right thing.
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