Static class properties (read-only)

Re: Static class properties (read-only)

In article <vj4v20o2qfi7c9 @corp.supernews .com>,
Greg Brunet <gregbrunet@NOS PAMsempersoft.c om> wrote:[color=blue]
>
>In puzzling over classes, I'm wondering if classes can have read-only
>static properties? I certainly seem to be able to do create static
>properties like this:
>
>class C(object):
> count = 0
>
> def __init__(self,s ):
> C.count += 1
> self.Name = s
>
> def __del__(self):
> C.count -= 1
>
>and C.count should have a count of the number of its instances that have
>been created. However, someone could set the value directly. I know
>that using get/set methods, I can make a read-only property at the
>object/instance level. Can this be done at the class level? Thanks,[/color]

Nope. Gotta do a metaclass. <evil grin>
--
Aahz (aahz@pythoncra ft.com) <*> http://www.pythoncraft.com/

This is Python. We don't care much about theory, except where it intersects
with useful practice. --Aahz

Re: Static class properties (read-only)


"Greg Brunet" <gregbrunet@NOS PAMsempersoft.c om> wrote in message
news:vj4v20o2qf [email protected] news.com...[color=blue]
> In puzzling over classes, I'm wondering if classes can have[/color]
read-only[color=blue]
> static properties? I certainly seem to be able to do create static
> properties like this:
>
> class C(object):
> count = 0
>
> def __init__(self,s ):
> C.count += 1
> self.Name = sCC
>
> def __del__(self):
> C.count -= 1
>
> and C.count should have a count of the number of its instances that[/color]
have[color=blue]
> been created. However, someone could set the value directly.[/color]

Prefixing count with a single underscore will tell others that is is
private-- they should not write it and should not depend on being able
to read it in future versions. Prefixing with 2 underscores will
invoke name-mangling, which you need to read about before using.

TJR

Re: Static class properties (read-only)

Greg Brunet wrote:
[color=blue]
> In puzzling over classes, I'm wondering if classes can have read-only
> static properties? I certainly seem to be able to do create static
> properties like this:
>
> class C(object):
> count = 0
>
> def __init__(self,s ):
> C.count += 1
> self.Name = s
>
> def __del__(self):
> C.count -= 1
>
> and C.count should have a count of the number of its instances that have
> been created. However, someone could set the value directly. I know
> that using get/set methods, I can make a read-only property at the
> object/instance level. Can this be done at the class level? Thanks,[/color]

Yes, you can make a class have a read-only property, but you can do this
only by using a custom metaclass. Once you do make it read-only, of
course, nobody can set it, including methods such as __init__ & __del__!-)


Alex