HackerRank Set .add() problem solution in python

In this Set .add() problem solution in python If we want to add a single element to an existing set, we can use the .add() operation. It adds the element to the set and returns ‘None’. Apply your knowledge of the .add() operation to help your friend Rupal. Rupal has a huge collection of country stamps. She decided to count the total number of distinct country stamps in her collection. She asked for your help. You pick the stamps one by one from a stack of N country stamps. Find the total number of distinct country stamps.

Problem solution in Python 2 programming.

n = int(raw_input())
stamp = set()
for i in range(n):
  stamp.add(raw_input())
print len(stamp)

Problem solution in Python 3 programming.

# Enter your code here. Read input from STDIN. Print output to STDOUT
a = set()
[a.add(input()) for _ in range(int(input()))]
print(len(a))

Problem solution in pypy programming.

n = int(raw_input())
estampas = [raw_input() for i in range(n)]

print len(set(estampas))

Problem solution in pypy3 programming.

# Enter your code here. Read input from STDIN. Print output to STDOUT
num  = int(input())
country = set([])
for i in range(num):
    country.add(input())
print(len(list(country)))