input: Write a python function to generate the first n prime numbers.
  assert generate_prime_numbers(5) == [2, 3, 5, 7, 11]
  assert generate_prime_numbers(3) == [2, 3, 5]
  assert generate_prime_numbers(8) == [2, 3, 5, 7, 11, 13, 17, 19]
output: def generate_prime_numbers(n):
      if n <= 0:
          return []
      primes = []
      num = 2
      while len(primes) < n:
          for p in primes:
              if num % p == 0:
                  break
          else:
              primes.append(num)
          num += 1
      return primes