python - 传递给 exec() 或 eval() 的代码不会将调用类的类名视为当前类

Question

我在看这篇文章:https://docs.python.org/3/tutorial/classes.html#private-variables

请有人举一个例子来帮助我理解以下引用:

Notice that code passed to exec() or eval() does not consider the classname of the invoking class to be the current class; this is similar to the effect of the global statement, the effect of which is likewise restricted to code that is byte-compiled together. The same restriction applies to getattr(), setattr() and delattr(), as well as when referencing dict directly.

Answer 1

它基本上是在告诉你双下划线的“魔法”不适用于 exec或 eval ，因此请考虑以下示例:

>>> class Foo:
...     def __init__(self):
...         self.__bar = 42
...     def method0(self):
...         return self.__bar * 2
...     def method1(self):
...         return eval('self.__bar * 2')
...
>>> f = Foo()
>>> f.method0()
84
>>> f.method1()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 7, in method1
  File "<string>", line 1, in <module>
AttributeError: 'Foo' object has no attribute '__bar'

同样，对于 getattr等等:

>>> getattr(f, '__bar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Foo' object has no attribute '__bar'