input: Write a function to merge two sorted lists and return the merged list in sorted order. The function should handle lists of any length, including empty lists.
  assert merge_sorted_lists([2,4,6], [3,5,7])==[2,3,4,5,6,7]
  assert merge_sorted_lists([1,3,5], [2,4,6])==[1,2,3,4,5,6]
  assert merge_sorted_lists([], [2,4,6])==[2,4,6]
  
output: def merge_sorted_lists(list1, list2):
      merged_list = []
      i, j = 0, 0
      while i < len(list1) and j < len(list2):
          if list1[i] < list2[j]:
              merged_list.append(list1[i])
              i += 1
          else:
              merged_list.append(list2[j])
              j += 1
      merged_list.extend(list1[i:])
      merged_list.extend(list2[j:])
      return merged_list