code: def _handle_exists(self, node, scope, ctxt, stream):
          
          res = fields.Int()
          try:
              self._handle_node(node.expr, scope, ctxt, stream)
              res._pfp__set_value(1)
          except AttributeError:
              res._pfp__set_value(0)
          return res
docs: Handle the exists unary operator
  
          :node: TODO
          :scope: TODO
          :ctxt: TODO
          :stream: TODO
          :returns: TODO