Ricardo Aráoz wrote:
> So lets take it a notch up.
> Wanted to change the mfunc method but ONLY for an instance, not a class:
>
>>>> MyObj = MyClass()
>>>> MyObj.mfunc(data)
> pre change behavior
>>>> MyObj.mfunc = newfunc
>>>> MyObj.mfunc(data)
> Traceback (most recent call last):
> File "<input>", line 1, in <module>
> TypeError: newfunc() takes exactly 2 arguments (1 given)
I believe the correct way to do this is to use the __get__() method of
the function object to create a bound method and assign that to the
instance attribute:
In [13]: class MyClass(object): pass
....:
In [14]: myObj = MyClass()
In [15]: def newfunc(self):
....: print 'post change behavior'
....:
....:
All functions are descriptors. The __get__() method returns a bound method:
In [16]: newfunc.__get__?
Type: method-wrapper
Base Class: <type 'method-wrapper'>
String Form: <method-wrapper '__get__' of function object at 0x20a6cb0>
Namespace: Interactive
Docstring:
descr.__get__(obj[, type]) -> value
In [17]: newfunc.__get__(myObj, MyClass)
Out[17]: <bound method MyClass.newfunc of <__main__.MyClass object at
0x20ba950>>
Assigning the bound method to myObj.mfunc has the desired behaviour:
In [18]: myObj.mfunc = newfunc.__get__(myObj, MyClass)
In [19]: myObj.mfunc()
post change behavior
I have a writeup of descriptors here:
http://personalpages.tds.net/~kent37/kk/00008.html
You can also use types.MethodType to do the same thing:
In [20]: from types import MethodType
In [21]: MethodType(newfunc, myObj, MyClass)
Out[21]: <bound method MyClass.newfunc of <__main__.MyClass object at
0x20ba950>>
Kent
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