Replace class instance with function inside the class (python)

Question

I want to replace the class instance "model" with a new instance. This should happen in a reset function inside the class. I could easily do model = Model(number = 2) outside of the class, but that is not what I need.

The number thing is just an easy example for you. My actual task is totally different. In summary I need to create a new instance with the same name, because I need a new run of the __init__. And this has to happen inside the reset function. I hope you understand what I mean. My reset function does not work unfortunately:

class Model():
    def __init__(self, number):
        self.number = number

    def reset(self):
        self = Model(number = 2)

model = Model(number = 1)
print(model.number) #it is 1

model.reset()
print(model.number) #it is 1 aswell, should be 2 :(

You cannot change the identity of an object, if that is what you are asking. You can mutate your object to have the same relevant values, in this case, reset would simply do self.number=2. But why isn't mode = Model(2) what you need, precisely? — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 19, 2020 at 9:16
You just ended up assigning newly created instance to a local variable self. You cannot replace object with another object in-place. You reset should really just set the instance to its desired / initial state by setting its attributes. — Ondrej K.
– Ondrej K., Commented Jun 19, 2020 at 9:16

dvec · Accepted Answer · 2020-06-19 09:15:57Z

2

You can't reassign self iside of your class, but you can do something like that:

class Model():
    def __init__(self, number):
        self.number = number

    def reset(self):
        self.__dict__ = Model(number = 2).__dict__

model = Model(number = 1)
print(model.number) #it is 1

model.reset()
print(model.number) #it is 2 :)

3 Comments

Thomas Schillaci Over a year ago

What about calling the __init__ method instead?

timgeb Over a year ago

This is not creating a new instance though, which might be important.

juanpa.arrivillaga Over a year ago

Why do this? Why not just self.number = 2. Note, this breaks shared-key namespace dicts...

Maximus93 · Accepted Answer · 2020-06-19 09:48:40Z

1

What about this here? Is it allowed to run the init manual in the reset function?

class Model():
    def __init__(self, number):
        self.number = number

    def reset(self):
        self.__init__(2)

model = Model(number = 1)
print(model.number) #it is 1

model.reset()
print(model.number) #it is 2 now

answered Jun 19, 2020 at 9:48

Maximus93

294 bronze badges

Comments

timgeb · Accepted Answer · 2020-06-19 09:20:18Z

0

I want to replace the class instance "model" with a new instance.

All you have to do is to rebind the name model.

Use

model = Model(number=2)

or

model = Model(model.number + 1)

If you want to increment number automatically on instantiation, you could use something like this:

class Model:
    counter = 1

    def __init__(self):
        self.number = Model.counter
        Model.counter += 1

answered Jun 19, 2020 at 9:20

timgeb

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