replace a method in class: how?

[Brian Blais]

Hello,

I want to replace a method in a class during run-time with another function. I tried
the obvious, but it didn't work:

class This(object):
def update(self,val ):
print val

def another_update( obj,val):
print "another",v al

t=This()
t.update(5)
t.update=anothe r_update
t.update(5) # this one doesn't work, gives
# TypeError: another_update( ) takes exactly 2 arguments (1 given)


clearly it isn't seeing it as a method, just an attribute which happens to be a
function. Is there a preferred way to do this?


thanks,

Brian Blais


--
-----------------

bblais@bryant.e du

http://web.bryant.edu/~bblais

[John Machin]

Re: replace a method in class: how?

On 27/06/2006 9:14 AM, Brian Blais wrote:[color=blue]
> Hello,
>
> I want to replace a method in a class during run-time with another
> function. I tried the obvious, but it didn't work:
>
> class This(object):
> def update(self,val ):
> print val
>
> def another_update( obj,val):
> print "another",v al
>
> t=This()
> t.update(5)
> t.update=anothe r_update
> t.update(5) # this one doesn't work, gives
> # TypeError: another_update( ) takes exactly 2 arguments (1 given)
>
>
> clearly it isn't seeing it as a method, just an attribute which happens
> to be a function. Is there a preferred way to do this?
>[/color]

You have a strange definition of "obvious". You say you want to replace
a method in a *class*, not in an instance of that class ... so just do that:

|>> class This(object):
.... def update(self,val ):
.... print val
....
|>> def another_update( obj,val):
.... print "another",v al
....
|>> This.update = another_update
|>> t = This()
|>> t.update(42)
another 42

Cheers,
John

[Bruno Desthuilliers]

Re: replace a method in class: how?

Brian Blais a écrit :[color=blue]
> Hello,
>
> I want to replace a method in a class during run-time with another
> function. I tried the obvious, but it didn't work:
>
> class This(object):
> def update(self,val ):
> print val
>
> def another_update( obj,val):
> print "another",v al
>
> t=This()
> t.update(5)
> t.update=anothe r_update[/color]

This is not "replacing a method in a class", but replacing it in an
instance.
[color=blue]
> t.update(5) # this one doesn't work, gives
> # TypeError: another_update( ) takes exactly 2 arguments (1 given)[/color]
[color=blue]
>
> clearly it isn't seeing it as a method, just an attribute which happens
> to be a function. Is there a preferred way to do this?[/color]

import types
t.update = types.MethodTyp e(another_updat e)

[nate]

Re: replace a method in class: how?

I don't know a ton about this, but it seems to work if you use:
This.update = another_update
(instead of t.update = another_update)
after saying This.update = another_update, if you enter This.update, it
says <unbound method This.another_up date>, (it's unbound)
but if you call
t.update(5)
it will print:
another 5

[Maric Michaud]

Re: replace a method in class: how?

Le mardi 27 juin 2006 05:05, Bruno Desthuilliers a écrit :[color=blue]
> import types
> t.update = types.MethodTyp e(another_updat e)[/color]

This works with :

t.update = types.MethodTyp e(another_updat e, t)

Oh, this *really* misleading what the intent of the programmer is, and

In [29]: t.update
Out[29]: <bound method ?.<lambda> of <__main__.a instance at 0xa774d96c>>

all let think it's a method defined in t's class.
I prefer early binding with default parameters :

In [30]: def another_update( self, param) :pass
....:

In [31]: t.update = lambda x, self=t : another_update( self, x)

In [32]: t.update = lambda x, self=t, func=another_up date : func(self, x)

In [33]: t.update
Out[33]: <function <lambda> at 0xa7744aac>

So we have a function and know it (probably) belongs to the instance.

--
_____________

Maric Michaud
_____________

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Tel: +33 426 880 097

[Bruno Desthuilliers]

Re: replace a method in class: how?

Maric Michaud a écrit :[color=blue]
> Le mardi 27 juin 2006 05:05, Bruno Desthuilliers a écrit :
>[color=green]
>>import types
>>t.update = types.MethodTyp e(another_updat e)[/color]
>
>
> This works with :
>
> t.update = types.MethodTyp e(another_updat e, t)[/color]

oops ! too fast on the send button :(
And thanks for the correction.