Q.Suppose annual day of your school is to be celebrated. The school has decided to felicitate those parents of the students studying in classes XI and XII, who are the alumni of the same school. In this context, answer the following questions:

Think of the membership of a school club. Nobody can be a member twice — either your name is on the roll or it is not — and the roll has no meaningful order; alphabetical or not, the club is the same club. A set is precisely this idea made formal: a collection defined only by which distinct things belong to it. Duplicates are meaningless, order is meaningless, membership is everything.

Once two clubs exist, natural questions appear, and they are the classic set operations:

• Union — everyone who is in either club (or both). The combined invitation list.
• Intersection — everyone who is in both clubs at once. The people with a scheduling clash.
• Difference — members of the first club who are not in the second. Note the direction matters: A minus B is not B minus A.
• Symmetric difference — people in exactly one of the two clubs, never both.

Python builds this directly into the language. A set is written in curly braces, or made from any collection with set() — and any duplicates vanish on entry:

music = {"Asha", "Ravi", "Meena"}
drama = {"Ravi", "Farhan"}

print(music | drama)    # union
print(music & drama)    # intersection: {'Ravi'}
print(music - drama)    # difference
print("Asha" in music)  # True — membership test

The practical properties that follow from the definition:

• Elements are unique. Turning a list into a set is the standard one-line way to strip duplicates: set([1, 2, 2, 3]) becomes {1, 2, 3}.
• Elements are unordered, so a set cannot be indexed or sliced — there is no "first" member. …