Accessing variables by reference in python

Question

I am not sure if this makes any sense in python, but consider I have two variables x and y:

x = 1
y = x

Now, at a later time when I change x, I want y to see this change. that is if I do

x = 2

I want y to be 2 also. Is there a way to do reference(x) = 2, so that all variables that were assigned to x will see this change?

One way to make this work is to use lists for everything as described here. This would work if I had defined x as list, so if

x = [1]
y = x

then, doing x.clear() and x.append(val) for val in new_list would work, and y will change according to the new list.

But I would like to do it for any type, because otherwise I will need to revisit most of my codebase. Is there a mutable type so I don't have to redefine all my y's to be x[0].

Any suggestion is appreciated.

I don't understand why you would really want this semantic. Are you refactoring code from another language or something? — miradulo
– miradulo, Commented Feb 28, 2018 at 2:38
To put it in context, I have a PyQt tableView where its model has some data. Now, the model's data (type or value) might be changed by the user at any time. I have threads running in the background which use the table's model data from the program start. If a user changes the data, I would rather it be reflected automatically in the other threads and classes without rereading the model. — Gerges
– Gerges, Commented Feb 28, 2018 at 2:42
I don't understand you problem that much. You means the y=copy.deepcopy(x)？ — Windyground
– Windyground, Commented Feb 28, 2018 at 2:44
Possible duplicate of Passing an integer by reference in Python — damores
– damores, Commented Feb 28, 2018 at 3:03
@damores not really... I mentioned that answer as possible solution, but i was looking for something different. I suppose the lazy way out I am asking for is just not possible. — Gerges
– Gerges, Commented Feb 28, 2018 at 3:08

user19650 · Accepted Answer · 2018-02-28 02:44:21Z

4

Perhaps make a small wrapper class for your values? The object containing the value is then passed "by reference".

class Wrapper:
    def __init__(self, value):
        self.value = value

x = Wrapper(5)
y = x

print(x.value, y.value)
x.value = 3
print(x.value, y.value)

Output:

5 5
3 3

answered Feb 28, 2018 at 2:44

user19650

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