Global variables within classes.

[Bruno Desthuilliers]

Kevac Marko a écrit :
> On Nov 10, 8:39 pm, Marc 'BlackJack' Rintsch <bj_... at gmx.net> wrote:
>> Don't think so.  It's a surprise for many but then class attributes are
>> not that common in code or they even use this "gotcha" for
>> immutable default values.  As long a the value isn't changed the default
>> value is just referenced from the class then and not every instance.
>>
> 
> When changing default value, is there any way to change class
> attribute and all referenced attributes too?
> 
> class M:
>     name = u"Marko"
> 
> a, b = M(), M()
> a.name = u"Kevac"
> print M.name, a.name, b.name
> -> Marko Kevac Marko
> 
> Is there any way to get here -> Kevac Kevac Kevac ?

class ClassAttribute(object):
   """
   If you dont understand this code, google for
   +python +descriptor +protocol
   """
   def __init__(self, attrname, default=""):
     self.attrname = attrname
     self.default = default

   def __get__(self, inst, cls):
     return getattr(cls, self.attrname, self.default)

   def __set__(self, inst, val):
     setattr(type(inst), self.attrname, val)

class M(object):
   name = ClassAttribute('_name', "Marko")

a, b = M(), M()
a.name = u"Kevac"
print M.name, a.name, b.name

HTH