input: Write a python function to generate prime numbers between 2 and 20.
  assert generate_primes() == [2, 3, 5, 7, 11, 13, 17, 19]
output: def generate_primes():
      primes = []
      for num in range(2, 21):
          is_prime = True
          for i in range(2, int(num ** 0.5) + 1):
              if num % i == 0:
                  is_prime = False
                  break
          if is_prime:
              primes.append(num)
      return primes