input: Write a function to construct a nested loop in Python that takes a list of lists and prints out each element combination in a new line. The function should accept a list of lists as input and return the output as per the example provided.
  assert print_nested_lists([[1, 2, 3], [4, 5, 6], [7, 8, 9]])==None
  # Expected output:
  # 1 4 7
  # 1 4 8
  # 1 4 9
  # 1 5 7
  # 1 5 8
  # 1 5 9
  # 1 6 7
  # 1 6 8
  # 1 6 9
  # 2 4 7
  # 2 4 8
  # 2 4 9
  # 2 5 7
  # 2 5 8
  # 2 5 9
  # 2 6 7
  # 2 6 8
  # 2 6 9
  # 3 4 7
  # 3 4 8
  # 3 4 9
  # 3 5 7
  # 3 5 8
  # 3 5 9
  # 3 6 7
  # 3 6 8
  # 3 6 9
  assert print_nested_lists([[10], [20], [30]])==None
  # Expected output:
  # 10 20 30
output: def print_nested_lists(lst):
      for i in lst[0]:
          for j in lst[1]:
              for k in lst[2]:
                  print(i, j, k)