Destroy object method after first invocation

Question

I have already figured out the answer to that, so I am placing it here as a question to myself - for the sake of those that may come up with similar question.

Basically, I wanted to be able to delete an object method. The reason?

I have an action that has to be executed once per object life. This action cannot be placed in the __init__ method since I need system fully initialized before it is performed.

I have a suitable place holder for that action - a method existing in the parent class. But I would like to be able to avoid checking the condition every time the method is called by framework.

So I tried this approach:

In [193]: class Parent(object): def place_for_action(self): print 'This is parent' .....: In [194]: class Child(Parent): def place_for_action(self): super(Child, self).place_for_action() print 'This is child' delattr(self, 'place_for_action') .....:

When I tried it, I failed

In [186]: c= Child() In [187]: c.place_for_action() This is child --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) /homes/markg/<ipython-input-187-da53ac96ffa9> in <module>() ----> 1 c.place_for_action() /homes/markg/<ipython-input-185-7037db53bd87> in do_once(self) 2 def place_for_action(self): 3 print 'This is child' ----> 4 delattr(self, 'place_for_action') 5 AttributeError: 'Child' object attribute 'place_for_action' is read-only

What? Why can't you do it at the end of __init__? What other instantiation is required? — jonrsharpe
– jonrsharpe, Commented Sep 18, 2014 at 13:36
@jonrsharpe It is a complex graphical implementation. The action is to send signals to other components of the system, and there's no guarantee that the components are initialized at the time — volcano
– volcano, Commented Sep 18, 2014 at 13:39
I'm dubious that this is necessary, but it's hard to tell without seeing more of your actual code. — chepner
– chepner, Commented Sep 18, 2014 at 13:58
@chepner, there's such a thing as "existing design constraint". Do you have a better answer to the question? I will be happy to see it. — volcano
– volcano, Commented Sep 18, 2014 at 14:28
I don't because I don't know what your design constraints are, hence my comment rather than an actual answer. — chepner
– chepner, Commented Sep 18, 2014 at 14:30

volcano · Accepted Answer · 2014-09-18 13:27:39Z

OK, the answer was - delete method at the class level - which suits my need

In [195]: class Child(Parent): def place_for_action(self): super(Child, self).place_for_action() print 'This is child' delattr(self.__class__, 'place_for_action') .....:

Works like charm

In [196]: c = Child() In [197]: c.place_for_action() This is parent This is child In [198]: c.place_for_action() This is parent

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