docs: def to_dictionary(
              self,
              key_selector=lambda item: item.key,
              value_selector=list):
          """Build a dictionary from the source sequence.
  
          Args:
              key_selector: A unary callable to extract a key from each item.
                  By default the key of the Grouping.
  
              value_selector: A unary callable to extract a value from each item.
                  By default the value is the list of items from the Grouping.
  
          Note: This method uses immediate execution.
  
          Raises:
              ValueError: If the Queryable is closed.
              TypeError: If key_selector is not callable.
              TypeError: If value_selector is not callable.
          """
          return super(Lookup, self).to_dictionary(key_selector, value_selector)