Default values of arguments with the same id

[DrVictor]

class test:
    def __init__(self,val=[]):
        self.val=val

a=test()
b=test()
print(id(a.val)==id(b.val)) #True

I noticed that the default value of the arguments has the same id as other instances.
And by changing that value, it changes for other instances.

a.val+=[12]
print(b.val) # [12]

Is this normal for you?