input: Write a function to generate prime numbers between 1 and a given number n. If n is less than 2, the function should print an empty list.
  assert generate_prime_numbers(20)==[2, 3, 5, 7, 11, 13, 17, 19]
  assert generate_prime_numbers(1)==[]
  assert generate_prime_numbers(0)==[]
  assert generate_prime_numbers(2)==[2]
  assert generate_prime_numbers(30)==[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
output: def generate_prime_numbers(n):
      if n < 2:
          return []
      primes = []
      for num in range(2, n + 1):
          for i in range(2, int(num**0.5) + 1):
              if num % i == 0:
                  break
          else:
              primes.append(num)
      return primes