code: def visit_UnaryOperation(self, node):
          
          if node.op.nature == Nature.PLUS:
              return +self.visit(node.right)
          elif node.op.nature == Nature.MINUS:
              return -self.visit(node.right)
          elif node.op.nature == Nature.NOT:
              return Bool(not self.visit(node.right))
docs: Visitor for `UnaryOperation` AST node.