Cumulative product of a list.

  Args:
    l: a list of integers
  Returns:
    a list with one more element (starting with 1)

def _cumprod(l):
  """Cumulative product of a list.

  Args:
    l: a list of integers
  Returns:
    a list with one more element (starting with 1)
  """
  ret = [1]
  for item in l:
    ret.append(ret[-1] * item)
  return ret