code: def _gen_code(self):
          
          # This is the dictionary that stores all the generated code.
  
          self.code = {}
          def match_key(expr):
              if type(expr) is dict:
                  code = {}
                  for key in expr.keys():
                      code[key] = match_key(expr[key])
              else:
                  arg_list = [e for e in expr.atoms() if e.is_Symbol]
                  code = self._expr2code(arg_list, expr)
              return code
  
          self.code = match_key(self.expressions)
docs: Generate code for the list of expressions provided using the common sub-expression eliminator to separate out portions that are computed multiple times.