input: Write a function to find the common elements between two given lists. Then return the list of common elements.
  def find_common_elements(list1, list2):
      common = [x for x in list1 if x in list2]
      return common
  assert find_common_elements([1, 2, 3], [2, 3, 4])==[2, 3]
output: def find_common_elements(list1, list2):
      common = [x for x in list1 if x in list2]
      return common