Mutable v.s. Immutable

There are two types of objects^[1]:

• immutable: objects can't be changed.
• mutable: objects can be changed.

Let's see an example: int is immutable, if we tried to modify this value with addition, then you'd get a new object.

>>> x = 5
>>> id(x)
9793216
>>> x += 1
>>> id(x)
9793248 # a new object

>>> a = "test"
>>> id(a)
139661423109424
>>> a += "_test"
>>> id(a)
139661423109552 # a new object
>>> 

Consider with a mutable object, like list:

>>> a = [1,2,3]
>>> id(a)
140586760807680
>>> a.append(10)
>>> id(a)
140586760807680 # still the same memory address
>>>