属性和普通变量使用增强赋值语句时的差异

1.API中相关描述

2.示例

1

num = 4class Test:    num = 3    def f(self):        self.num += 2        print(self.num) # 5        num += 3 # UnboundLocalError: local variable 'num' referenced before assignment        print(num)x = Test()x.f()'''为什么self.num += 2正常执行,num += 3报错?这里为方便,忽略增强赋值语句和普通赋值语句的差异,从普通赋值语句分析既问题变为：为什么self.num = self.num + 2正常执行而num = num + 3报错？1.对于类对象属性或实例对象的数据属性    1.右边的num可能是类属性或实例对象的数据属性    2.左边的num是实例的数据属性,在必要时会自动创建2.对于普通变量    左右两边的num最终均会被解析为局部变量'''

再来点补充知识：

9.2. Python Scopes and Namespaces

A special quirk of Python is that – if no global statement is in effect – assignments to names always go into the innermost scope. Assignments do not copy data — they just bind names to objects. The same is true for deletions: the statement del x removes the binding of x from the namespace referenced by the local scope. In fact, all operations that introduce new names use the local scope: in particular, import statements and function definitions bind the module or function name in the local scope.