code: def append(self, node):
      
      if not isinstance(node, grammar.STATEMENTS):
        raise ValueError
      self.to_append[-1].append(node)
docs: Append a statement to the current statement.
  
      Note that multiple calls to append will result in the last statement to be
      appended to end up at the bottom.
  
      Args:
        node: The statement to append.
  
      Raises:
        ValueError: If the given node is not a statement.