How to bound a method to a instance ?

[Emmanuel]

Hi,


I would like to know how to bound a method to a instance of a class.

One application would be to allow a change in a method after a reload :

module toto :
--------------
class toto:
def method(self):
(...)


main module :
--------------
import toto

a = toto.toto()
a.method() -> does something ...

reload (toto)
now a is not reloaded...

a.method = toto.toto().method
does not work, because a.method would be bounded to a new instance...


Thanks,

Emmanuel...

 

[=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?=]

main module :
--------------
import toto

a = toto.toto()
a.method() -> does something ...

reload (toto)
now a is not reloaded...

a.method = toto.toto().method
does not work, because a.method would be bounded to a new instance...

It might be best to change the class of a:

reload (toto)
a.__class__ = toto.toto

Then, a.method will automatically become the new method. Of course,
this will also change all other methods of toto, not just method.

If you really want to change only method, you could do

a.__class__.__dict__['method'] = toto.toto.__dict__['method']

That would change just method, but of all instances of the old
definition of toto.toto.

If you really want to change only one method, and only of one
object, you need to use new.instancemethod:

a.method = new.instancemethod(toto.toto.method.im_func, a, a.__class__)

Regards,
Martin

 

[Emmanuel]

Wonderfull !!

I thank you very much for this clear explanation...

Emmanuel

=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?= a écrit :

main module :
--------------
import toto

a = toto.toto()
a.method() -> does something ...

reload (toto)
now a is not reloaded...

a.method = toto.toto().method
does not work, because a.method would be bounded to a new instance...

It might be best to change the class of a:

reload (toto)
a.__class__ = toto.toto

Then, a.method will automatically become the new method. Of course,
this will also change all other methods of toto, not just method.

If you really want to change only method, you could do

a.__class__.__dict__['method'] = toto.toto.__dict__['method']

That would change just method, but of all instances of the old
definition of toto.toto.

If you really want to change only one method, and only of one
object, you need to use new.instancemethod:

a.method = new.instancemethod(toto.toto.method.im_func, a, a.__class__)

Regards,
Martin

 

[Maarten van Reeuwijk]

It might be best to change the class of a:

reload (toto)
a.__class__ = toto.toto

Thank you emmanuel for asking this question, I was wondering exactly the
same thing. Is it also possible to override the reload method to make it
(besides reloading) to scan through all namespaces for objects of class
toto.toto and replace their methods automatically? What would that code
look like?

Thanks,

Maarten

 

[=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?=]

Thank you emmanuel for asking this question, I was wondering exactly the
same thing. Is it also possible to override the reload method to make it
(besides reloading) to scan through all namespaces for objects of class
toto.toto and replace their methods automatically? What would that code
look like?

In general, it is impossible or atleast very inefficient to do that.
It may be easiest if toto.toto would prepare itself for reloading:

import weakref
try:
weakref.totos
except AttributeError:
weakref.totos = []

class toto:
def __init__(self, args):
weakref.totos.append(weakref.ref(self))
...

def update_totos():
for t in weakref.totos:
t = t()
if t: t.__class__ = toto

def shrink_totos():
totos = []
for t in weakref.totos:
if t(): totos.append(t)
weakref.totos=[]

Then, after reloading toto, invoke toto.update_totos(). From
time to time, invoke weakref.shrink_totos(), to discard unused
weak references.

If you absolutely want to update all objects without preparing
a list earlier, you can use gc.get_objects() to find all containers;
you need to find out which of those are totos. Don't compare the
classes of the objects for identity (o.__class__ is toto.toto), unless
you have a reference of the old class (i.e. before reloading).

Regards,
Martin

 

[Josiah Carlson]

def shrink_totos():

totos = []
for t in weakref.totos:
if t(): totos.append(t)
weakref.totos=[]

^^ should be totos

- Josiah