input: Write a function to return a sublist consisting of the prime numbers from a given list of integers. If no prime numbers are found, return an empty list. If the list is empty, return an empty list as well.
  
  def is_prime(num):
      if num <= 1:
          return False
      for i in range(2, num // 2 + 1):
          if num % i == 0:
              return False
      return True
  
  def prime_list(lst):
      prime_lst = []
      for num in lst:
          if is_prime(num):
              prime_lst.append(num)
      return prime_lst
  
  assert prime_list([2, 8, 3, 6, 10, 7, 14, 11, 17, 15]) == [2, 3, 7, 11, 17]
  assert prime_list([4, 6, 8, 9, 10, 12, 14, 15, 16, 18]) == []
  assert prime_list([]) == []
output: def prime_list(lst):
      prime_lst = []
      for num in lst:
          if is_prime(num):
              prime_lst.append(num)
      return prime_lst