def __setitem__(self, k, v):
        try:
            if self[k] is v:
                return # ALREADY SAVED.  NOTHING TO DO!
        except __HOLE__: # NOT PRESENT, SO JUST SAVE THE VALUE
            dict.__setitem__(self, k, v)
            return
        raise KeyError('attempt to overwrite existing key!')
dataset/ETHPy150Open cjlee112/pygr/pygr/mapping.py/KeepUniqueDict.__setitem__