class Something:

    saved_data = [2, 3, 4, 5]

    def __init__(self):
        self.data = Something.saved_data
        self.data2 = [x for x in Something.saved_data]

x = Something()

print(x.data is Something.saved_data)
print(x.data2 is Something.saved_data)

(Jul-26-2020, 02:32 PM)ifigazsi Wrote: I have a class variable, but I want to change this at instance level, without changing the original class variable, how can i make it

(Jul-26-2020, 03:20 PM)buran Wrote:

(Jul-26-2020, 02:32 PM)ifigazsi Wrote: I have a class variable, but I want to change this at instance level, without changing the original class variable, how can i make it

This looks like wrong design - if you want and are going to change it at instance level why it should be class attributee - it should be instance attribute.

class Something:

    def __init__(self):
        self.saved_data = [2,3,4,5]
        self.data_to_work_with = self.saved_data
        self.data_to_work_with2 = [x for x in self.saved_data]

x = Something()

print(x.data_to_work_with is x.saved_data)
print(x.data_to_work_with2 is x.saved_data)

class Something:
 
    data = [2, 3, 4, 5]
 
    def __init__(self):
        self.reset_data()

    def reset_data(self):
        self.data = Something.data[:]
 
something = Something()
 
something.data.append(6)
print(Something.data, something.data)
something.reset_data()
print(Something.data, something.data)

Output:
[2, 3, 4, 5] [2, 3, 4, 5, 6]
[2, 3, 4, 5] [2, 3, 4, 5]

(Jul-26-2020, 04:03 PM)Yoriz Wrote: Something like this ?

class Something:
 
    data = [2, 3, 4, 5]
 
    def __init__(self):
        self.reset_data()

    def reset_data(self):
        self.data = Something.data[:]
 
something = Something()
 
something.data.append(6)
print(Something.data, something.data)
something.reset_data()
print(Something.data, something.data)

Output:
[2, 3, 4, 5] [2, 3, 4, 5, 6]
[2, 3, 4, 5] [2, 3, 4, 5]

(Jul-26-2020, 05:43 PM)deanhystad Wrote: Good or bad design depends on the problem you are trying to solve. Global variables are usually bad, but sometimes they can lead to an elegant solution for the right kind of problems. Using a class with no instances is usually bad, but it can be an elegant way to implement a singleton.

With no information about your problem it is impossible to say if any design is good or bad.

class Workshop:

    def __init__(self, name):
        self.name = name
        self.components_data = ['d2', 'f3', 'g4', 'h5']
        self.refill_all_components()

    def refill_all_components(self):
        self.components_available = self.components_data[:]
        self.components_used = []

    def use_a_component(self):
        from random import shuffle
        shuffle(self.components_available)
        self.components_used.append(self.components_available.pop())

    def __repr__(self):
        return (f'{self.name} components left: {self.components_available} components used: {self.components_used}')

workshop1 = Workshop('Unit1')
workshop2 = Workshop('Unit2')
workshop3 = Workshop('Unit3')

for i in range(2):
    workshop1.use_a_component()
print(workshop1)
workshop1.refill_all_components()
print(workshop1)

(Jul-27-2020, 02:57 PM)deanhystad Wrote: It is not a common practice to hid import statements inside a function. They should all appear at the top of the file unless you are trying to get around a circular reference problem.

As I said before, you cannot judge design in a vacuum. If this design works well for solving your problem, it is a good design. I can say that is is not a generic solution. This would never be a module that others can use to solve their problem. Components should be generic. An inventory control system would never have a "refill_all_components" method. It might have method(s) to check inventory numbers and aid in ordering, but "get everything right now" is unrealistic. In an inventory system the components would be more than just a string, they would be objects. The inventory system would know how to communicate with objects to let you know if a component was available or when a component was available.

Is this a good design? Maybe yes. Maybe no.