code: def fold(self, elems):
          
  
          cond, if_true, if_false = elems
  
          if isinstance(cond, Constant):
              return [if_true if cond.value else if_false]
  
          return [Instructions([cond, JumpIfNot(len(if_true) + 2), pop, if_true,
                                Jump(len(if_false) + 1), pop, if_false])]
docs: Perform constant folding.  If the result of applying the
          operator to the elements would be a fixed constant value,
          returns the result of applying the operator to the operands.
          Otherwise, returns an instance of ``Instructions`` containing
          the instructions necessary to apply the operator.
  
          :param elems: A list (or list-like object) containing the
                        elements.
  
          :returns: A list of one element, containing the instructions
                    necessary to implement the operator.