Re: [Python-ideas] 'const' statement

18 Jan 2013

      On Fri, Jan 18, 2013 at 7:01 PM, Paul Moore  wrote:
...
Named values are obviously a good thing, but I see little benefit, and
a lot of practical difficulty, with the idea of "enforced const-ness"
in Python.
FWIW, people can play whatever games they like by injecting arbitrary
objects into sys.modules.
...
...
...
class Locked:
...     def __setattr__(self, attr, value):
...         raise AttributeError("Rebinding not permitted")
...     def __delattr__(self, attr):
...         raise AttributeError("Deletion not permitted")
...     attr1 = "Hello"
...     attr2 = "World"
...
sys.modules["example"] = Locked
import example
example.attr1
'Hello'
example.attr2
'World'
example.attr2 = "Change"
example.attr2 = "World"
sys.modules["example"] = Locked()
import example
example.attr1
'Hello'
example.attr2
'World'
example.attr2 = "Change"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __setattr__
AttributeError: Rebinding not permitted
The import system is even defined to expressly permit doing this in a
*module's own code* by replacing "sys.module[__name__]" with a
different object.

So, any such proposal needs to be made with the awareness that anyone
that *really* wants to do this kind of thing already can, but they
don't.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan@gmail.com   |   Brisbane, Australia