code: def discard(self, key):
          
          if key in self:
              i = self.map[key]
              del self.items[i]
              del self.map[key]
              for k, v in self.map.items():
                  if v >= i:
                      self.map[k] = v - 1
docs: Remove an element.  Do not raise an exception if absent.
  
          The MutableSet mixin uses this to implement the .remove() method, which
          *does* raise an error when asked to remove a non-existent item.