Agree that what you are looking for may not be a good idea. So make
sure you don't shoot yourself in the foot with it. You should
probably look into your problem some more.
>>> def once(obj,attrname,value):
... if hasattr(obj,attrname):
... return
... else:
... setattr(obj,attrname,value)
...
>>> class Foo:
... pass
...
>>> foo = Foo()
>>> once(foo,"a",1)
>>> foo.a
1
>>> once(foo,"b",2)
>>> foo.a
1
>>> def m1(self):
... print "i am m1"
...
>>> def m2(self):
... print "i am m2"
...
>>> once(Foo,"mx",m1)
>>> foo.mx()
i am m1
>>> once(Foo,"mx",m2)
>>> foo.mx()
i am m1
>>>
This is very generic code, but you could make it specific to a class
and an attribute. If so look into properties.
class Foo2:
def _setMyAttr(self,value):
if hasattr(self,"_myAttr"):
return
self._myAttr = value
def _getMyAttr(self):
if not hasattr(self,"_myAttr"):
return "somedefaultvalue"
return self._myAttr
myAttr = property(_getMyAttr,_setMyAttr)
Note also : stay away from __setattr__ until you know what you are
doing and
you know when to use self.__dict__ assignments. Painful personal
experiences for me.
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