Why is a dictionary as an attribute not unique?

Question

Python

class SomeClass:
    attr_dic = {'a': 1, 'b': 2}

some_a = SomeClass()
some_b = SomeClass()

some_a.attr_dic['a'] = 3
some_b.attr_dic['b'] = 4

print some_a.attr_dic
print some_b.attr_dic

This code outputs

{'a': 3, 'b': 4}
{'a': 3, 'b': 4}

How to make the dictionary unique, poke into the documentation.

Answer 1

class SomeClass:
    def __init__(self):
        self.attr_dic = {'a': 1, 'b': 2}

Answer 2

It seems to me that in this case, the attr_dic variable defined in the SomeClass class, when using this class, remains common for all objects of this class (clumsily written, but illustrative example in python 3):

class SomeClass:
    attr_dic = {'a': 1, 'b': 2}
class OtherClass:
    def __init__(self):
        self.attr_dic={'a':1,'b':2}
some_a = SomeClass()
some_b = SomeClass()
print('some_a adress %i'%id(some_a)) #выведет 204146672
print('some_b adress %i'%id(some_b)) # выведет 204148720
print('some_a dict adress %i'%id(some_a.attr_dic)) # 204166128
print('some_b dict adress %i'%id(some_b.attr_dic)) # 204166128
other_a = OtherClass() 
other_b = OtherClass()
print('other_a adress %i'%id(other_a)) #204145392
print('other_b adress %i'%id(other_b)) #204148592
print('other_a dict adress %i'%id(other_a.attr_dic)) #204165448
print('other_b dict adress %i'%id(other_b.attr_dic)) #204115000

Answer 3

Because you need to read literature. You declare a class variable. It will be common to all instances of your class. And they are used, for example, to store information needed by all instances.