input: Write a function to find the common elements in two lists. The function should take two lists as input and return a list of common elements. If there are no common elements, the function should return an empty list. 
  
  assert find_common_elements([3, 9, 15, 21, 27], [21, 7, 13, 29, 31])==[21]
  assert find_common_elements([1, 2, 3, 4, 5], [6, 7, 8, 9, 10])==[]
  assert find_common_elements([], [21, 7, 13, 29, 31])==[]
  assert find_common_elements([3, 9, 15, 21, 27], [])==[]
  assert find_common_elements([1, 1, 1, 1], [1, 1, 1, 1])==[1, 1, 1, 1]
output: def find_common_elements(list1, list2):
      return [item for item in list1 if item in list2]