Why is a set not taking tuple (where dictionary is an item) as a key?-CodePudding

I understand that set keys are immutable, hence data types like lists are not eligible for being a key in the set. In the example shown below why can a tuple not work as a key if a dictionary is present inside the tuple? Can somebody help me with an explanation?

x= (1,{'a':1})
y= (1,2)
print(type(x),type(y))

# piece of code which is not giving me an error is below
set1 = {x,'INDIA'}

# set 2 can be created in similar manner without an error
set2 = {y,'INDIA'}

set2

CodePudding user response：

Well, because x is indeed mutable! x[1] is refers to the dict, which is a mutable object.

x = (1, {'a':1})
print(x)
x[1]['a'] = 'BANANA'
print(x)

Output:

(1, {'a': 1})
(1, {'a': 'BANANA'})

CodePudding user response：

A tuple can only serve as a key if all elements of the tuple can serve as a key. A dict cannot serve as a key (because it is mutable).

The more technical answer here is that dict keys must be hashable, and that tuples are only hashable if their individual elements are hashable.