code: def nunique(self, axis=0, dropna=True):
          
          axis = self._get_axis_number(axis) if axis is not None else 0
          return self._reduce_dimension(
              self._query_compiler.nunique(axis=axis, dropna=dropna)
          )
docs: Return Series with number of distinct
             observations over requested axis.
  
          Args:
              axis : {0 or 'index', 1 or 'columns'}, default 0
              dropna : boolean, default True
  
          Returns:
              nunique : Series