replace mothod for only one object but not for a class

Bruno Desthuilliers bdesth.quelquechose at free.quelquepart.fr
Tue Oct 14 18:28:35 CEST 2008


George Sakkis a écrit :
> On Oct 14, 1:50 pm, hofer <bla... at dungeon.de> wrote:
>> Hi,
>>
>> I have multiple objects all belonging to the same class
>>  (which I didn't implement and whose code I don't want to modify)
>>
>> Now I'd like to change one method for one object only (after it has
>> been created) without adding any overhead
>> to the call of the other object's methods.
>>
>> Is this possible?
>>
>> Example
>> ##### This is NOT what I'd like to do
>> ##### as it overwrites the method for all objects of this class
>> o1 = aclass()
>> o2 = aclass()
>> # call original method
>> o1.method()
>> o2.method()
>> # overwrite the method for the entire class
>> aclass.method = mymethod
>> o1.method() # now new method
>> o2.method() # now new method
>>
>> ####### What doesn't work, but what I'd like to do
>> o1 = aclass()
>> o2 = aclass()
>> # call original method
>> o1.method()
>> o2.method()
>> # overwrite the method for the entire class
>> o1.method = mymethod
>> o1.method() # now new method
>> o2.method() # still old method
>>
>> thanks for any pointers.
> 
> Please post the actual code that doesn't work. The following works as
> expected:
> 
>     >>> class A(object):
>     ...     def foo(self): return 'Original'
>     ...
>     >>> a = A()
>     >>> b = A()
>     >>> a.foo()
>     'Original'
>     >>> b.foo()
>     'Original'
>     >>> b.foo = lambda: 'Modified'
>     >>> a.foo()
>     'Original'
>     >>> b.foo()
>     'Modified'

Except that b.foo is a plain function, not a method:

 >>> class A(object):
...     def foo(self): return "original called on %s" % self
...
 >>> a = A()
 >>> b = A()
 >>> a.foo()
'original called on <__main__.A object at 0xb7c0c56c>'
 >>> b.foo()
'original called on <__main__.A object at 0xb7c0c4ec>'
 >>> b.foo = lambda: "modified called on %s" % self
 >>> b.foo
<function <lambda> at 0xb7bfe9cc>
 >>> b.foo()
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "<stdin>", line 1, in <lambda>
NameError: global name 'self' is not defined
 >>> b.foo = lambda self: "modified called on %s" % self
 >>> b.foo()
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: <lambda>() takes exactly 1 argument (0 given)
 >>>




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