A tuple is immutable but it may contain mutable objects. In larger hierarchies of objects it may become less obvious whether down the lines, there is some mutable object somewhere in the data tree.
One can define a recursive function to check for immutability manually. However first, it may not be as efficient as if it was built-in. Second, the existence of a built-in function 'isimmutable' puts the concept of immutability some more into the spotlight. You might indeed implement some personal 'policy for copy/deepcopy'. But, how can you prevent the insertion of an object into the data tree which does not follow your copy/deepcopy convention? As soon as you allow members of type 'tuple' you must either check recursively or only allow ints and strings as tuple members. -- https://mail.python.org/mailman/listinfo/python-list
