Apparently ast_error_finish calls PyTuple_GetItem with a value that is not a tuple, but a SyntaxError instance (in Python/ast.c line 112).  It seems that ast_error_finish expects that PyErr_Fetch will return the exception value as a tuple, and in some cases this seems correct (for example when not in an except clause), but not in this case.  I don't know much about Python exception handling in C, but it seems to me, that it shouldn't expect always a tuple (see also http://docs.python.org/dev/py3k/c-api/exceptions.html#PyErr_NormalizeException).