On 30/04/19 5:11 AM, Steven D'Aprano wrote:
On Tue, Apr 30, 2019 at 12:47:02AM +0530, Arup Rakshit wrote:
I really didn't write that code by myself. The day I'll you will not see
me here everyday :) . I was watching a PyCon video
https://youtu.be/81S01c9zytE?t=8172 where the author used this code. But
his explanation is not clear to me. The main problem is that the guy who
was recorded it far away from the projector, so what speaker were
showing there is not clear. So thought to ask here as usual. Because I
felt so lost with this trick.
Okay, the short, SIMPLIFIED (and therefore inaccurate) summary of
descriptors:
Descriptors are the "magic" used by Python whenever it does an attribute
lookup. When you do any sort of attribute lookup or assignment:
x = spam.eggs
spam.eggs = value
Python looks at spam and spam's class for an attribute called "eggs",
and if that attribute is an object with a __set__ or __get__ method, it
calls that method:
x = spam.eggs
=> x = spam.eggs.__get__()
spam.eggs = value
=> spam.eggs.__set__(value)
For the gory details of what *precisely* happens, see the Howto Guide:
https://docs.python.org/3/howto/descriptor.html
All answers in the thread with the howto link above helped me to
understand this at least. I did't masters yet, but atleast now can
reason about what is going on when I meet such code examples.
Python has a few common descriptors built in:
- ordinary methods
- classmethod
- staticmethod
- property
Apart from staticmethod, they're all pretty common in code. But writing
your own custom descriptors is fairly rare. I've only done it once, in
25+ years of using Python.
Thank you very much.
--
Thanks,
Arup Rakshit
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor
