Declarative properties

George Sakkis george.sakkis at gmail.com
Fri Oct 12 01:04:27 CEST 2007


On Oct 11, 7:48 am, Artur Siekielski <artur.siekiel... at gmail.com>
wrote:

> I know about 'property' function in Python, but it's normal usage
> isn't declarative, because I have to code imperatively getters and
> setters:
>
> class Person(object):
>    def __init__(self, name):
>       self._name = name
>    def _get_name(self):
>       return self._name
>    def _set_name(self, new_name):
>       self._name = new_name
>    name = property(_get_name, _set_name)
>
> I would like to have something like that:
>
> class Person(object):
>    name = property('_name')

By now you must have been convinced that default getters/setters is
not a very useful idea in Python but this does not mean you can't do
it; it's actually straightforward:

def make_property(attr):
    return property(lambda self: getattr(self,attr),
                    lambda self, value: setattr(self, attr, value))

class Person(object):
   name = make_property('_name')
   def __init__(self, name):
       self.name = name

You could take it even further by removing the need to repeat the
attribute's name twice. Currently this can done only through
metaclasses but in the future a class decorator would be even better:

def PropertyMaker(*names, **kwds):
    format = kwds.get('format', '_%s')
    def meta(cls,bases,attrdict):
        for name in names:
            attrdict[name] = make_property(format % name)
        return type(cls,bases,attrdict)
    return meta

class Person(object):
    __metaclass__ = PropertyMaker('name', format='__%s__')

    def __init__(self, name):
        self.name = name
        print self.__name__


George




More information about the Python-list mailing list