When would sum( ) not work for tuples ?

Sum would not work for the following cases:

• When tuple does not have numeric value.
  For example:-
  tup = ("a", "b")
  tup_sum = sum(tup)
  TypeError: unsupported operand type(s) for +: 'int' and 'str'

here, "a" and "b" are string not integers therefore they can not be added together.

• Nested tuples having tuple as element.
  For example:-

a = (1,2,(3,4))  
print(sum(a))  

Output:
TypeError: unsupported operand type(s) for +: 'int' and 'tuple'

Here, tuple 'a' is a nested tuple and since it consist of another tuple i.e. (3,4) it's elements can not be added to another tuple. Hence it will throw an error.

• Tuple containing elements of different data type.
  For example:-

a = (1,2.5,(3,4),"hello")  
print(sum(a))  

Output:
TypeError: unsupported operand type(s) for +: 'float' and 'tuple'

Tuple a contains elements of integer, float, string and tuple type which can not be added together.