code: def site_properties(self):
          
          props = {}
          prop_keys = set()
          for site in self:
              prop_keys.update(site.properties.keys())
  
          for k in prop_keys:
              props[k] = [site.properties.get(k, None) for site in self]
          return props
docs: Returns the site properties as a dict of sequences. E.g.,
          {"magmom": (5,-5), "charge": (-4,4)}.