code: def select_fields(self, fields):
          
  
          if (type(fields) is str):
              fields = [fields]
          if not isinstance(fields, list) or not all(type(x) is str for x in fields):
              raise TypeError('\"fields\" must be a str or list[str]')
  
          vfields = self.__proxy__.get_vertex_fields()
          efields = self.__proxy__.get_edge_fields()
          selected_vfields = []
          selected_efields = []
          for f in fields:
              found = False
              if f in vfields:
                  selected_vfields.append(f)
                  found = True
              if f in efields:
                  selected_efields.append(f)
                  found = True
              if not found:
                  raise ValueError('Field \'%s\' not in graph' % f)
  
          with cython_context():
              proxy = self.__proxy__
              proxy = proxy.select_vertex_fields(selected_vfields)
              proxy = proxy.select_edge_fields(selected_efields)
              return SGraph(_proxy=proxy)
docs: Return a new SGraph with only the selected fields. Other fields are
          discarded, while fields that do not exist in the SGraph are ignored.
  
          Parameters
          ----------
          fields : string | list [string]
              A single field name or a list of field names to select.
  
          Returns
          -------
          out : SGraph
              A new graph whose vertex and edge data are projected to the selected
              fields.
  
          See Also
          --------
          get_fields, get_vertex_fields, get_edge_fields
  
          Examples
          --------
          >>> from turicreate import SGraph, Vertex
          >>> verts = [Vertex(0, attr={'breed': 'labrador', 'age': 5}),
                       Vertex(1, attr={'breed': 'labrador', 'age': 3}),
                       Vertex(2, attr={'breed': 'vizsla', 'age': 8})]
          >>> g = SGraph()
          >>> g = g.add_vertices(verts)
          >>> g2 = g.select_fields(fields=['breed'])