def findAnEven(l):
  """
  Assumes l is a list of ints

  Returns the first even num in l
  
  Raises ValueError if l doesn't contain an even num
  """

  first_even_n = 0

  for num in l:
    if num % 2 == 0:
      first_even_n = num
      break
  
  if first_even_n == 0:
    raise ValueError("l doesn't contain an even number")
  else:
    return first_even_n