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Strategies when hunting for dictionary corruption

I'm wrapping some C++ libraries using pybind11. On the pybind11 side of
things, I've written a simple type converter between Python's datetime.date
objects and our internal C++ date objects. The first thing the type
converter needs to do is to insure that the datetime C API is initialized:

    if (!PyDateTimeAPI) { PyDateTime_IMPORT; }

This is failing because a dictionary internal to the import mechanism is
being corrupted, the extensions dict in import.c. I highly doubt this is a
Python issue. It's much more likely to be a bug in our C++ libraries or in

The problem is, dictionaries being rather dynamic objects (growing and
sometimes shrinking), the actual data location which might be corrupted
isn't fixed, but can move around. I've got a Python interpreter configured
using --with-pydebug, it's compiled with -ggdb -O0, and I'm ready to watch
some memory locations, but it's not clear what exactly I should watch or
how/when to move my watchpoint(s) around. Should I not be thinking in terms
of watchpoints? Is there a better way to approach this problem? (I also
have valgrind at my disposal, but am not very skilled in its use.)