What happened in this class
scarblac at pino.selwerd.nl
Sun Dec 31 06:13:01 EST 2000
Emile van Sebille <emile at fenx.com> wrote in comp.lang.python:
> I saw Pearu's lazy extension and built and installed it on
> my linux system(recent cvs). I thought I'd see how it
> played in a class vs getattr and got this result. Thinking
> something broke along the way, I then switched over to the
> win95 system(2.0 #8), and got the same thing. This doesn't
> happen under 1.52.
> class test:
> def __getattr__(self, name):
> return "egs"
> t = test()
> print dir(t)[1:5]
> ['e', 'g', 'g', 's']
> Now I know this is contrived, but I still didn't expect
> these results. Should I have?
Real weird. dir(t) returns ['e', 'e', 'g', 'g', 's', 's']. It's pretty
simple to find out what it actually calls by adding another print
def __getattr__(self, name):
['e', 'e', 'g', 'g', 's', 's']
So here we see that apparently dir() in 2.0 works by calling the __members__
and __methods__ special functions, and they both return "egs", and since
dir() was expecting a list it reads that as ['e','g','s'], adds them
together, and sorts them.
These special functions are *not* documented in chapter 3 of the 2.0
language reference and I suppose that is wrong. They don't look like the
sort of thing you would want to change though. Or maybe they can be useful,
if you define a data member by means of __getattr__ but you still want it
to show up in dir(). Needs docs.
In conclusion, making a __getattr__ that returns something completely
regardless of the name you put in is not a good idea :-)
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