code: def keys(self):
          '''Return all valid keys'''
          keys = []
          for key, value in self.map.items():
              if isinstance(value, Shovel):
                  keys.extend([key + '.' + k for k in value.keys()])
              else:
                  keys.append(key)
          return sorted(keysf keys(self):
          '''Return all valid keys'''
          keys = []
          for key, value in self.map.items():
              if isinstance(value, Shovel):
                  keys.extend([key + '.' + k for k in value.keys()])
              else:
                  keys.append(key)
          return sorted(keys)
docs: Return all valid keys