input: Write a function to find the common elements between two lists and return a new list containing those elements.
  
  assert common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10])==[2, 8]
  assert common_elements([1, 2, 3], [4, 5, 6])==[]
  assert common_elements([1, 2, 2, 3], [2, 2, 4])==[2, 2]
  assert common_elements([], [1, 2, 3])==[]
  assert common_elements([1, 2, 3], [])==[]
output: def common_elements(list1, list2):
      return [item for item in list1 if item in list2]