code: def get_substrates(self, material_id, number=50, orient=None):
          
          req = "/materials/{}/substrates?n={}".format(material_id, number)
          if orient:
              req += "&orient={}".format(" ".join(map(str, orient)))
          return self._make_request(req)
docs: Get a substrate list for a material id. The list is in order of
          increasing elastic energy if a elastic tensor is available for
          the material_id. Otherwise the list is in order of increasing
          matching area.
  
          Args:
              material_id (str): Materials Project material_id, e.g. 'mp-123'.
              orient (list) : substrate orientation to look for
              number (int) : number of substrates to return;
                  n=0 returns all available matches
          Returns:
              list of dicts with substrate matches