python constants -- http://code.activestate.com/recipes/65207-constants-in-python/

const.py

# Put in const.py...:
class _const:
 class ConstError(TypeError):
   pass
 def __setattr__(self,name,value):
   if self.__dict__.has_key(name):
     raise self.ConstError, "Can't rebind const(%s)"%name
   self.__dict__[name]=value
import sys
sys.modules[__name__]=_const()

# that's all -- now any client-code can
import const
# and bind an attribute ONCE:
const.magic = 23
# but NOT re-bind it
const.magic = 88
# raises const.ConstError
# you may also want to add the obvious __delattr__