Concatenation and Memory Storage With Mutable and Immutable Objects (Mainly Tuples and Lists)

Hello,

I am building upon another thread that asked a similar question, however I feel the need to build off that in order to build my domain knowledge on this topic.

When creating a variable that is a tuple and concatenating with another tuple but storing that result in the same variable name prior to concatenation the object id types are different. This is expected since tuples are immutable and the original object is disposed of while the variable name is now referencing our new object. (Please see code snippet below)

obj1 = 1,2,3,4,5
print(id(obj1))
obj2= 6,7,8,9,10
obj1 = obj1+obj2
print(obj1)
print(id(obj1)) #The id of this object is not the same as when we printed it earlier (As expected)

However, when we follow the same process for lists the id of the object prior to concatenation and after is actually different. This is where I'm confused and please correct me If I am not thinking of this properly. However, since lists are mutable shouldn't concatenation modify the original object so in this case there is no actual disposal of the object prior to concatenation (and therefore no variable reassignment occurred). Therefore, shouldn't the object id's be the same?

list1 = [1,2,3,4]
list2 = [1,2,3,4]
print(id(list1))
list1 = list1 + list2
print(id(list1))