Static properties

Alex Martelli aleaxit at yahoo.com
Thu Aug 26 23:01:49 CEST 2004


Per Erik Stendahl <python-spam at berrs.net> wrote:

> Hello everyone,
> 
> Is it possible to define "static properties" in a class?

Yes, but only by defining a custom metaclass to be the type of that
class.  Properties are defined in the type, not in the instance; so, for
a class itself to have properties, the class's type, commonly known as
its metaclass, must be the one defining them.


>>> class metaPath(type):
...     def curdir(cls): return os.getcwd()
...     curdir = property(curdir)
... 
>>> class Path: __metaclass__ = metaPath
... 
>>> print Path.curdir
/Users/alex/cb/dblite/dblite_0.5


_However_...:

>>> print Path().curdir
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: 'Path' object has no attribute 'curdir'
>>> 

if you want to be able to get at property curdir on INSTANCES of Path as
you normally would for a staticmethod, yet with property syntax, I think
you need to get a bit more clever than this... descriptors don't get
looked up two metalevels up, only one...


Alex



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