def _spline(t, p0, p1, p2, p3):
    """
    Catmull-Rom cubic spline to interpolate 4 given points.

    :param t: Time index through the spline (must be 0-1).
    :param p0: The previous point in the curve (for continuity).
    :param p1: The first point to interpolate.
    :param p2: The second point to interpolate.
    :param p3: The last point to interpolate.
    """
    return (
        t * ((2 - t) * t - 1) * p0
        + (t * t * (3 * t - 5) + 2) * p1
        + t * ((4 - 3 * t) * t + 1) * p2
        + (t - 1) * t * t * p3) / 2


class Path(object):
    """
    Class to record and play back the motion of a Sprite.
    """

    def __init__(self):
        """
        No specific parameters.  To define a Path, use the methods to jump to
        a location, wait or move between points.
        """
        self._steps = []
        self._index = None
        self._rec_x = 0
        self._rec_y = 0
        self.reset()

    def reset(self):
        """
        Reset the Path for use next time.
        """
        self._index = 0

    def next_pos(self):
        """
        :return: The next position tuple (x, y) for the Sprite on this path.
        """
        result = None
        if self._index <= len(self._steps):
            result = self._steps[self._index]
            self._index += 1
        return result

    def is_finished(self):
        """
        :return: Whether this path has got to the end.
        """
        return self._index >= len(self._steps)

    def _add_step(self, pos):
        """
        Add a step to the end of the current recorded path.

        :param pos: The position tuple (x, y) to add to the list.
        """
        self._steps.append(pos)
        self._rec_x = pos[0]
        self._rec_y = pos[1]

    def wait(self, delay):
        """
        Wait at the current location for the specified number of iterations.

        :param delay: The time to wait (in animation frames).
        """
        for i in range(0, delay):
            self._add_step((self._rec_x, self._rec_y))

    def jump_to(self, x, y):
        """
        Jump straight to the newly specified location - i.e. teleport there and
        don't create a path to get there.

        :param x:  X coord for the end position.
        :param y: Y coord for the end position.
        """
        self._add_step((x, y))

    def move_straight_to(self, x, y, steps):
        """
        Move straight to the newly specified location - i.e. create a straight line
        Path from the current location to the specified point.

        :param x:  X coord for the end position.
        :param y: Y coord for the end position.
        :param steps: How many steps to take for the move.
        """
        start_x = self._rec_x
        start_y = self._rec_y
        for i in range(1, steps+1):
            self._add_step((
                int(start_x + (x - start_x) / float(steps) * i),
                int(start_y + (y - start_y) / float(steps) * i)))

    def move_round_to(self, points, steps):
        """
        Follow a path pre-defined by a set of at least 4 points.  This Path will
        interpolate the points into a curve and follow that curve.

        :param points: The list of points that defines the path.
        :param steps: The number of steps to take to follow the path.
        """
        # Spline interpolation needs a before and after point for the curve.
        # Duplicate the first and last points to handle this.  We also need
        # to move from the current position to the first specified point.
        points.insert(0, (self._rec_x, self._rec_y))
        points.insert(0, (self._rec_x, self._rec_y))
        points.append(points[-1])

        # Convert the points into an interpolated set of more detailed points.
        steps_per_spline = steps / (len(points) - 3)
        for j in range(1, len(points) - 2):
            for t in range(1, steps_per_spline+1):
                y = _spline(float(t) / steps_per_spline,
                            float(points[j - 1][1]),
                            float(points[j][1]),
                            float(points[j + 1][1]),
                            float(points[j + 2][1]))
                x = int(points[j][0] + ((points[j + 1][0] - points[j][0]) *
                                        float(t) / steps_per_spline))
                self._add_step((x, int(y)))

@@ -617,24 +617,190 @@
 f a Sprite.%0A
+    %0A    The Screen will reset() the Path before iterating through each position usin%0A    next_pos() and checking whether it has reached the end using is_finished().%0A
     %22%22%22%0A%0A   
@@ -842,33 +842,8 @@
     
-  No specific parameters.
   To
@@ -884,24 +884,16 @@
  jump to
-%0A       
  a locat
@@ -910,16 +910,25 @@
 or move 
+%0A        
 between 

Clarify use of Path objects.