Dynamic class methods misunderstanding

Hans Nowak hans at zephyrfalcon.org
Fri Jan 28 17:09:16 CET 2005


Bill Mill wrote:
> Hello all,
> 
> I have a misunderstanding about dynamic class methods. I don't expect
> this behavior:
> 
> In [2]: class test:
>    ...:      def __init__(self, method):
>    ...:         self.method = method
>    ...:         self.method()
>    ...:
> 
> In [3]: def m(self): print self
>    ...:
[...]
> 
> TypeError: m() takes exactly 1 argument (0 given)
> -----------------------------------------------------------------------------
> 
> Why doesn't m get the implicit self parameter in the self.method()
> call? How would I make it a proper member of the class, so that a
> self.method() call would work with the above "m" function?

m is a function.  When you assign it to self.method, it's still a 
function.  You don't create a new method that way; all you have is a new 
attribute called 'method' containing the function.

To add m as a new method to the *class*, do this:

 >>> class test:
...     def __init__(self, method):
...         self.__class__.method = method
...         self.method()
...
 >>> def m(self): print self
...
 >>> test(m)
<__main__.test instance at 0x0192ED78>
<__main__.test instance at 0x0192ED78>
 >>>

To add m as a new method to the *instance*, use new.instancemethod, as 
Diez B. Roggisch already pointed out.

HTH,

-- 
Hans Nowak
http://zephyrfalcon.org/




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