code: def n_exec_stmt(self, node):
          
          self.write(self.indent, 'exec ')
          self.preorder(node[0])
          if not node[1][0].isNone():
              sep = ' in '
              for subnode in node[1]:
                  self.write(sep); sep = ", "
                  self.preorder(subnode)
          self.println()
          self.prune()
docs: exec_stmt ::= expr exprlist DUP_TOP EXEC_STMT
          exec_stmt ::= expr exprlist EXEC_STMT