AttributeError from Context __del__

[cjdrake]

This exception was observed by shader@ while testing the precedence repo:

Exception ignored in: <bound method Context.__del__ of <boolexpr.wrap.Context object at 0x7ffff2dc1400>>                                                                                             
Traceback (most recent call last):
  File "/usr/lib64/python3.4/site-packages/boolexpr/wrap.py", line 295, in __del__
AttributeError: 'NoneType' object has no attribute 'boolexpr_Context_del'
Exception ignored in: Exception ignored in: Exception ignored in: Exception ignored in: <bound method Context.__del__ of <boolexpr.wrap.Context object at 0x7ffff1a68d30>>                           
Traceback (most recent call last):
  File "/usr/lib64/python3.4/site-packages/boolexpr/wrap.py", line 295, in __del__
AttributeError: 'NoneType' object has no attribute 'boolexpr_Context_del'

The boolexpr_Context_del method is only called on object destruction, so we need to investigate the robustness of the C++/Python layer for handling Context objects.

[cjdrake]

Okay, I think I misunderstood this error when I first looked at it.

The object that is None is the lib object, returned from ffi.dlopen(libpath).

This is an odd failure. Is something over-writing boolexpr.lib ? Is it some strange interaction between pytest and Python's garbage collector?