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2011年6月4日 Benjamin Peterson <report@bugs.python.org>:
> 2011年6月4日 Soren Hansen <report@bugs.python.org>:
>> So my question is: If this change stays (which seems clear given that the only changes proposed here are ways of relaxing the type requirement of the __dir__ method's return value, not reverting the change altogether), and I have an old-style class with a __getattr__ defined, how do I make that class return whatever it would have usually returned for __dir__()?
>
> Yes, this is a limitation of magic methods on old style classes. The
> usual method is something like this:
>
>  def __getattr__(self, name):
>    if name == "__dir__":
>      return self.__dir__
>    # Other stuff
>
> Of course, the best fix is to use new-style classes. :)
If I do this:
===== test.py ======
class Foo:
 def __getattr__(self, name):
 if name == '__dir__':
 return self.__dir__
 return 'something else'
a = Foo()
print dir(a)
====================
After a lot of this:
 File "test.py", line 4, in __getattr__
 return self.__dir__
 File "test.py", line 4, in __getattr__
 return self.__dir__
 File "test.py", line 4, in __getattr__
 return self.__dir__
...I end up with a "RuntimeError: maximum recursion depth exceeded". I
can't say I'm surprised :)