Question

I’m trying to make a class that is borg-like. I’d like one particular property to be shared by all the instances, but other properites I would like to be unique to the instance. Here is what I have so far:

class SharedFacility:
  _facility = None

  def __init__(self):
    entries = {'facility': self._facility}
    self.__dict__.update(entries) 

  def _getfacility(self):
    return self._facility

  def _setfacility(self, value):
    self._facility = value

  facility = property(_getfacility, _setfacility)


class Warning(SharedFacility):
  def __init__(self, warnlevel, warntext):
    SharedFacility.__init__(self)
    print "Warning.__init__()"
    self.warntext = warntext
    self.warnlevel = warnlevel

  def __call__(self):
    self.facility(self.warnlevel, self.warntext)


def functionOne(a,b):
  print 'functionOne: a=%s, b=%s' % (a,b)

def functionTwo(a,b):
  print 'functionTwo: a=%s, b=%s' % (a,b)

####################################################
w1 = Warning(1, 'something bad happened')
w1.facility = functionOne
w2 = Warning(5, 'something else bad happened')
import pdb; pdb.set_trace()

if w1.facility is w2.facility:
  print "They match!"

w1() # functionOne: a=1, b='something bad happened'
w2() # functionOne: a=5, b='something else bad happened'

w2.facility = functionTwo
if w1.facility is w2.facility:
  print "They match!"

w1() # functionTwo: a=1, b='something bad happened'
w2() # functionTwo: a=5, b='something else bad happened'

The above code does not work. I’d like w1.facility and w2.facility to be a reference to the same object, but w1.warntext and w2.warntext two be two different values. I’m working with python 2.4.3 (no sense in mentioning I upgrade because I can’t).

Solution:

class Warning(object):
  _facility = None

  def __init__(self, warnlevel, warntext):
    print "Warning.__init__()"
    self._warntext = warntext
    self._warnlevel = warnlevel

  def __call__(self):
    Warning._facility(self._warnlevel, self._warntext)

  def _getfacility(self):
    return Warning._facility

  def _setfacility(self, value):
    Warning._facility = value

  facility = property(_getfacility, _setfacility)

@staticmethod
def functionOne(a,b):
  print 'functionOne: a=%s, b=%s' % (a,b)

@staticmethod
def functionTwo(a,b):
  print 'functionTwo: a=%s, b=%s' % (a,b)

Answer 1

Here’s what I would do:

class BorgLike:
    _shared = 'default'
    def __init__(self, unique):
        self.unique = unique
    @property
    def shared(self):
        return BorgLike._shared
    @shared.setter
    def shared(self, value):
        BorgLike._shared = value

I hope you know how to use this example for your own purpose. I wasn’t really sure what you wanted with your code, so I refrained from guessing and wrote a minimal example.