def EntityKind(key):
  if key.path().element_list():
    return key.path().element_list()[-1].type()
  else:
    return ''
convert an object in a tuple of strings (even if it is not iterable,
dataset/ETHPy150Open AppScale/appscale/AppServer/google/appengine/ext/analytics/entity.py/EntityKind--crossover with--dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/graphics/mosaicplot.py/_tuplify