Are Class variables mutable? [duplicate]

Question

If I define a simple class

class someClass():
    var = 1

x = someClass()
someClass.var = 2

This will make x.var equal 2. This is confusing to be because normally something akin to this like:

a = 1
b = a
a = 2

will leave b intact as b==1. So why is this not the same with class variables? Where is the difference? Can call all class variables mutable? In a way the class variables work more like assigning a list to a=[1] and doing a[0]=2.

Basically the problem is how is x.var acessing someClass.var it must be something different then is used when two variables are set equal in python. What is happening?

No, that is the point. Essentially, when you do SomeClass.var and someInstance.var are not necessarily same thing. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 15, 2017 at 9:20
not at all this is about the fact that someClass.var = 2 changes x.var and how x.var is bound to the class variable compared to the normal functioning of variables in python — Kuhlambo
– Kuhlambo, Commented Jun 15, 2017 at 9:21
A picture is worth a thousand words: stackoverflow.com/a/34126204/476 — deceze
– deceze ♦, Commented Jun 15, 2017 at 9:28

Uriel · Accepted Answer · 2017-06-15 09:24:46Z

3

var is a static class variable of someClass.

When you reach out to get x.var, y.var or some_other_instance.var, you are accessing the same variable, not an instance derived one (as long as you didn't specifically assigned it to the instance as a property).

edited Jun 15, 2017 at 9:24

answered Jun 15, 2017 at 9:22

Uriel

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2 Comments

Kuhlambo Over a year ago

So then when I use x.var = 2 I basically create a new variable in x that shadows the variable in someClass in this instance?

deceze Over a year ago

@pindakaas Bingo!

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Are Class variables mutable? [duplicate]

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