Is it possible to delete a method from an object (not class) in python?

Question

I have a class with a few methods, some of which are only valid when the object is in a particular state. I would like to have the methods simply not be bound to the objects

Answer 1

Looks like the way to dir() works by default is:

dir(obj) == sorted(obj.__dict__.keys() + dir(obj.__class__))

(well, removing duplicates anyway)

So an approach would be:

class Wizard(object):
    def __init__(self):
        self.mana = 0

    def __dir__(self):
        natdir = set(self.__dict__.keys() + dir(self.__class__))
        if self.mana <= 0:
            natdir.remove("domagic")
        return list(natdir)

    def addmana(self):
        self.mana += 1

    def domagic(self):
        if self.mana <= 0:
            raise NotEnoughMana()
        print "Abracadabra!"
        self.mana -= 1

With the behaviour in Py2.6 being:

>>> wiz = Wizard()

>>> [x for x in dir(wiz) if not x.startswith("_")]
['addmana', 'mana']

>>> wiz.addmana()

>>> [x for x in dir(wiz) if not x.startswith("_")]
['addmana', 'domagic', 'mana']

>>> wiz.domagic()
Abracadabra!

>>> [x for x in dir(wiz) if not x.startswith("_")]
['addmana', 'mana']

>>> wiz.domagic()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 13, in domagic
__main__.NotEnoughMana

Answer 2

You can use a hack like that:

>>> class A(object):
...     def test(self):
...         print 'test'
... 
>>> a = A()
>>> def noattr(name):
...     raise AttributeError('no attribute %s' % name)
... 
>>> a.test = lambda *a, **k: noattr('test')
>>> a.test()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)

/Users/piranha/<ipython console> in <module>()

/Users/piranha/<ipython console> in <lambda>(*a, **k)

/Users/piranha/<ipython console> in noattr(name)

AttributeError: no attribute test

Of course, this gives you wrong traceback, but exception is the same. ;-)

Another (IMHO - better) way is to override __getattr__ and then put dispatch logic there, then you can use it like that:

>>> class A(object):
...     def __getattr__(self, name):
...         def inner(*args, **kwargs):
...             print args, kwargs
...         return inner
... 
>>> a = A()
>>> a.test
    <function inner at 0x1006c36e0>
>>> a.test('q')
('q',) {}