Currently, pickle.py in the stdlib is limited by the python call stack. 
For deeply recursive data structures, the default recursion limit of 1000 
is not enough. The patch attached modifies pickle.py to instead use a 
deque object as a call stack. Pickler.save and other methods that increase 
the recursion depth are now generators which may yield either another 
generator or None, where yielding a generator adds it to the call stack.