code: def slice(cls, *args, **kwargs):
          
          coords, hash_key = cls._canonical_key(args, kwargs)
          try:
              return cls._slice_cache[hash_key]
          except KeyError:
              pass
  
          Slice = cls._make_dataset(coords)
          cls._slice_cache[hash_key] = Slice
          return Slice
docs: Take a slice of a DataSetFamily to produce a dataset
          indexed by asset and date.
  
          Parameters
          ----------
          *args
          **kwargs
              The coordinates to fix along each extra dimension.
  
          Returns
          -------
          dataset : DataSet
              A regular pipeline dataset indexed by asset and date.
  
          Notes
          -----
          The extra dimensions coords used to produce the result are available
          under the ``extra_coords`` attribute.