Convert (width, height) or size -> point.Point.

def _to_point(dims):
  """Convert (width, height) or size -> point.Point."""
  assert dims

  if isinstance(dims, (tuple, list)):
    if len(dims) != 2:
      raise ValueError(
          "A two element tuple or list is expected here, got {}.".format(dims))
    else:
      width = int(dims[0])
      height = int(dims[1])
      if width <= 0 or height <= 0:
        raise ValueError("Must specify +ve dims, got {}.".format(dims))
      else:
        return point.Point(width, height)
  else:
    size = int(dims)
    if size <= 0:
      raise ValueError(
          "Must specify a +ve value for size, got {}.".format(dims))
    else:
      return point.Point(size, size)