Thank you for your valuable time, I have just started learning Python. I came across Mutable and Immutable objects. As far as I know mutable objects can be changed after their creation.
a = [1,2,3]
print(id(a))
45809352
a = [3,2,1]
print(id(a))
52402312
Then why id of the same list "a" gets changed when its values are changed.
your interpretation is incorrect.
When you assign a new list to a, you change its reference.
On the other hand you could do:
a[:] = [3,2,1]
and then the reference would not change.
mutable means that the content of the object is changed. for example a.append(4) actually make a equal to [1, 2, 3, 4], while on the contrary, appending to a string (which is immutable) does not change it, it creates a new one.
However, when you re-assign, you create a new object and assign it to a, you don't alter the existing content of a. The previous content is lost (unless refered-to by some other variable)
append method. You can only do string + "foo", which will create a new string, but so does [1,2,3] + [4]. str.replace might be a better example.
If you change a list, its id doesn't change. But you may do things that instead create a new list, and then it will also have a new id.
E.g.,
>>> l=[]
>>> id(l)
140228658969920
>>> l.append(3) # Changes l
>>> l
[3]
>>> id(l)
140228658969920 # Same ID
>>> l = l + [4] # Computes a new list that is the result of l + [4], assigns that
>>> l
[3, 4]
>>> id(l)
140228658977608 # ID changed
When you do
a = [3, 2, 1]
a.a variable.Being immutable doesn't mean you assign a new object, it means your original object can be changed "in place" for example via .append()
>>> my_list = [1,2,3]
>>> id(my_list)
140532335329544
>>> my_list.append(5)
>>> id(my_list)
140532335329544
>>> my_list[3] = 4
>>> my_list
[1, 2, 3, 4]
>>> id(my_list)
140532335329544
