def sparsify(d):
"""Improve dictionary sparsity.
The dict.update() method makes space for non-overlapping keys.
Giving it a dictionary with 100% overlap will build the same
dictionary in the larger space. The resulting dictionary will
be no more that 1/3 full. As a result, lookups require less
than 1.5 probes on average.
Example:
>>> import __builtin__
>>> sparsify(__builtin__.__dict__)
"""
e = d.copy()
d.update(e)