Adding method to object

[Thomas Guettler]

Hi!

How can I add a method to an object.
This code does not work:

class Foo:
def __init__(self):
self.counter=0

f=Foo()

def incr(self):
self.counter+=1

f.incr=incr

f.incr()

===> python extend.py
Traceback (most recent call last):
File "extend.py" , line 12, in ?
f.incr()
TypeError: incr() takes exactly 1 argument (0 given)

[Gonçalo Rodrigues]

Re: Adding method to object

On Wed, 03 Dec 2003 10:44:12 +0100, "Thomas Guettler"
<guettli@thom as-guettler.de> wrote:
[color=blue]
>Hi!
>
>How can I add a method to an object.
>This code does not work:
>
>class Foo:
> def __init__(self):
> self.counter=0
>
>f=Foo()
>
>def incr(self):
> self.counter+=1
>
>f.incr=incr
>
>f.incr()
>
>===> python extend.py
>Traceback (most recent call last):
> File "extend.py" , line 12, in ?
> f.incr()
>TypeError: incr() takes exactly 1 argument (0 given)[/color]

You have to call it like

f.incr(f)

If you want to leave out the f as arg (call it like an instance
method) then
[color=blue][color=green][color=darkred]
>>> import new
>>> help(new.instan cemethod)[/color][/color][/color]
Help on class instancemethod in module __builtin__:

class instancemethod( object)
| instancemethod( function, instance, class)
|
| Create an instance method object.
|
....

And

new.instancemet hod(incr, f, f.__class__)

Should do the trick.

With my best regards,
G. Rodrigues

[Peter Otten]

Re: Adding method to object

Thomas Guettler wrote:
[color=blue]
> How can I add a method to an object.[/color]

self is not passed automatically, if you call an instance attribute.
You can provide a default value instead:
[color=blue][color=green][color=darkred]
>>> class Foo:[/color][/color][/color]
.... def __init__(self):
.... self.counter = 0
....[color=blue][color=green][color=darkred]
>>> f = Foo()
>>> def incr(self=f):[/color][/color][/color]
.... self.counter += 1
....[color=blue][color=green][color=darkred]
>>> f.incr = incr
>>> f.incr()
>>> f.counter[/color][/color][/color]
1[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

If you have more than one instance with the same incr() method, you can wrap
it into a lambda:
[color=blue][color=green][color=darkred]
>>> g = Foo()
>>> g.incr = lambda self=g: incr(self)
>>> g.incr()
>>> g.incr()
>>> g.counter[/color][/color][/color]
2

Peter

[marco]

Re: Adding method to object

Is it possible to do the same thing for an attribut, instead of a method ?

i'd like to wrap an newAttribute to an oldAttribute one :
example:
i've got an instance "n" of an "xmlNode" class
i'd like to use "n.parentNo de" instead of "n.parent" ...


"Gonçalo Rodrigues" <op73418@mail.t elepac.pt> a écrit dans le message de
news: 72krsvcpeur8hhu 74s4bhlsq3bf60f u055@4ax.com...[color=blue]
> On Wed, 03 Dec 2003 10:44:12 +0100, "Thomas Guettler"
> <guettli@thom as-guettler.de> wrote:
>[color=green]
> >Hi!
> >
> >How can I add a method to an object.
> >This code does not work:
> >
> >class Foo:
> > def __init__(self):
> > self.counter=0
> >
> >f=Foo()
> >
> >def incr(self):
> > self.counter+=1
> >
> >f.incr=incr
> >
> >f.incr()
> >
> >===> python extend.py
> >Traceback (most recent call last):
> > File "extend.py" , line 12, in ?
> > f.incr()
> >TypeError: incr() takes exactly 1 argument (0 given)[/color]
>
> You have to call it like
>
> f.incr(f)
>
> If you want to leave out the f as arg (call it like an instance
> method) then
>[color=green][color=darkred]
> >>> import new
> >>> help(new.instan cemethod)[/color][/color]
> Help on class instancemethod in module __builtin__:
>
> class instancemethod( object)
> | instancemethod( function, instance, class)
> |
> | Create an instance method object.
> |
> ...
>
> And
>
> new.instancemet hod(incr, f, f.__class__)
>
> Should do the trick.
>
> With my best regards,
> G. Rodrigues[/color]

[Sean Ross]

Re: Adding method to object

"marco" <marc.lentz@ctr ceal.caisse-epargne.fr> wrote in message
news:bqkrsb$nf1 $2@s1.read.news .oleane.net...[color=blue]
> Is it possible to do the same thing for an attribut, instead of a method ?
>
> i'd like to wrap an newAttribute to an oldAttribute one :
> example:
> i've got an instance "n" of an "xmlNode" class
> i'd like to use "n.parentNo de" instead of "n.parent" ...[/color]
[snip]

# try this ...
n.parentNode = n.parent

HTH
Sean

[marco]

Re: Adding method to object

> > Is it possible to do the same thing for an attribut, instead of a method
?[color=blue][color=green]
> >
> > i'd like to wrap an newAttribute to an oldAttribute one :
> > example:
> > i've got an instance "n" of an "xmlNode" class
> > i'd like to use "n.parentNo de" instead of "n.parent" ...[/color]
> [snip]
>
> # try this ...
> n.parentNode = n.parent[/color]

i'll try,
but ... it s not dynamic ....

if n.parent change .... n.parentNode will not change ... it must be
re-affected ... not ?

[Sean Ross]

Re: Adding method to object


"marco" <marc.lentz@ctr ceal.caisse-epargne.fr> wrote in message
news:bql820$uka $1@s1.read.news .oleane.net...[color=blue][color=green][color=darkred]
> > > Is it possible to do the same thing for an attribut, instead of a[/color][/color][/color]
method[color=blue]
> ?[color=green][color=darkred]
> > >
> > > i'd like to wrap an newAttribute to an oldAttribute one :
> > > example:
> > > i've got an instance "n" of an "xmlNode" class
> > > i'd like to use "n.parentNo de" instead of "n.parent" ...[/color]
> > [snip]
> >
> > # try this ...
> > n.parentNode = n.parent[/color]
>
> i'll try,
> but ... it s not dynamic ....
>
> if n.parent change .... n.parentNode will not change ... it must be
> re-affected ... not ?
>[/color]

You're right. Sorry about that. Maybe you could use a property?

n.__class__.par entNode = property(lambda self: self.parent, ... etc ... )

This way you can get/set/del n.parent using n.parentNode, and changes
to n.parent will be reflect in n.parentNode.

There's probably another way, but I can't think of it at the moment...

Hope that's a little more helpful than the last suggestion,
Sean

[marco]

Re: Adding method to object

Sean Ross wrote:[color=blue]
> "marco" <marc.lentz@ctr ceal.caisse-epargne.fr> wrote in message
> news:bql820$uka $1@s1.read.news .oleane.net...
>[color=green][color=darkred]
>>>>Is it possible to do the same thing for an attribut, instead of a[/color][/color]
>
> method
>[color=green]
>>?
>>[color=darkred]
>>>>i'd like to wrap an newAttribute to an oldAttribute one :
>>>>example:
>>>>i've got an instance "n" of an "xmlNode" class
>>>>i'd like to use "n.parentNo de" instead of "n.parent" ...
>>>
>>>[snip]
>>>
>>># try this ...
>>>n.parentNo de = n.parent[/color]
>>
>>i'll try,
>>but ... it s not dynamic ....
>>
>>if n.parent change .... n.parentNode will not change ... it must be
>>re-affected ... not ?
>>[/color]
>
>
> You're right. Sorry about that. Maybe you could use a property?
>
> n.__class__.par entNode = property(lambda self: self.parent, ... etc ... )
>
> This way you can get/set/del n.parent using n.parentNode, and changes
> to n.parent will be reflect in n.parentNode.
>
> There's probably another way, but I can't think of it at the moment...
>
> Hope that's a little more helpful than the last suggestion,
> Sean
>
>
>[/color]

perfect ! it works like a charm
thanx a lot !

[Dave Benjamin]

Re: Adding method to object

In article <72krsvcpeur8hh u74s4bhlsq3bf60 fu055@4ax.com>, Gonçalo Rodrigues wrote:[color=blue]
> If you want to leave out the f as arg (call it like an instance
> method) then
>[color=green][color=darkred]
>>>> import new
>>>> help(new.instan cemethod)[/color][/color]
> Help on class instancemethod in module __builtin__:
>
> class instancemethod( object)
> | instancemethod( function, instance, class)
> |
> | Create an instance method object.
> |
> ...
>
> And
>
> new.instancemet hod(incr, f, f.__class__)
>
> Should do the trick.[/color]

I tried to bring this up several weeks ago but nobody replied, so I'm
bringing it up again. I still see people recommending "new.instanceme thod",
yet "help(new)" says that the "new" module is deprecated. The seemingly
identical "types.MethodTy pe" ought to be its replacement, even though I
think "new.instanceme thod" is more clear. If you stringify types.MethodTyp e,
it says "<type 'instancemethod '>". The help for instancemethod, above, says
that instancemethod is in the __builtin__ module, but it is neither a
builtin nor available in the __builtin__ module. This is confusing. Can we
decide on a community standard for the appropriate way to create new
instance methods, and resolve the documentation discrepancies?

Thankya kindly,
Dave

--
..:[ dave benjamin (ramenboy) -:- www.ramenfest.com -:- www.3dex.com ]:.
: d r i n k i n g l i f e o u t o f t h e c o n t a i n e r :