changing __call__ on demand

[Steven Bethard]

Stefan Behnel wrote:
> Is there a way to change __call__ after class creation?

Check out this thread on the topic:

http://mail.python.org/pipermail/python-list/2004-January/203142.html

Basically, the answer is no -- at least not on a per-instance basis. 
You can try something like:

py> class Test(object):
...     def __new__(cls):
...         cls.__call__ = cls.call1
...         return object.__new__(cls)
...     def call1(self):
...         print 'call1'
...     def __call__(self):
...         print '__call__'
...
py> Test()()
call1

But then the call method is changed for all instances:

py> class Test(object):
...     instances = 0
...     def __new__(cls):
...         if cls.instances == 1:
...             print "setting __call__"
...             cls.__call__ = cls.call1
...         cls.instances += 1
...         return object.__new__(cls)
...     def call1(self):
...         print 'call1'
...     def __call__(self):
...         print '__call__'
...
py> t1 = Test()
py> t1()
__call__
py> t2 = Test()
setting __call__
py> t2()
call1
py> t1()
call1

Steve