def rotate_tour(tour, start=0):
  """
  Rotate a tour so that it starts at the given ``start`` index. This is
  equivalent to rotate the input list to the left.

  Parameters
  ----------
  tour: list
    The input tour
  start: int, optional (default=0)
    New start index for the tour

  Returns
  -------
  rotated: list
    The rotated tour
  """
  idx = tour.index(start)
  if idx != 0:
    rotated = tour[idx:] + tour[:idx]
  else:
    rotated = tour
  return rotated