Why is the output different?

Question

a = {10, 20, 30, 40}
b = {40, 50, 60, 70}
a.difference(b)
print(a)
c = a.difference(b)
print(c)

output: {40, 10, 20, 30}
{10, 20, 30}

Answer 1

a.difference(b) => will not reflect changes by operation on original sets, it returns a new result set. So first time output is same as original set a.

2nd time, your are storing result of operation into variable c... so c is result of operation.....

Note: set doesnot maintain order of insertion of elements..