I am having trouble creating moving platforms in pygames. I am getting an error, can anyone help me out please?

Question

So I have just started to learn how to program and I have been trying to create this small game with moving platforms. I can get regular walls/platforms to work but I can't seem to figure out how to get these moving ones to work. I keep getting a traceback that looks like this:

Traceback (most recent call last):
  File "C:\Users\Jacob\Desktop\gametest.py", line 227, in <module>
    walls.update()
  File "C:\Python34\lib\site-packages\pygame\sprite.py", line 462, in update
    s.update(*args)
  File "C:\Users\Jacob\Desktop\gametest.py", line 111, in update
    hit = pygame.sprite.collide_rect(self, self.player)
  File "C:\Python34\lib\site-packages\pygame\sprite.py", line 1300, in collide_rect
    return left.rect.colliderect(right.rect)
AttributeError: 'NoneType' object has no attribute 'rect'

I think the problem has to do with some of these bits of code that I have but I am not completely sure.

class Wall(pygame.sprite.Sprite):

    def __init__(self, width, height):
        #creates the wall
        pygame.sprite.Sprite.__init__(self)

        self.image = pygame.Surface([width, height])
        self.image.fill(blue)

        self.rect = self.image.get_rect()


######################################################
class MovingEnemy(Wall):
    change_x = 0
    change_y=0

    boundary_top = 0
    boundary_bottom = 0
    boundary_left = 0
    boundary_right = 0

    player = None
    level = None

    def update(self):
        # Move left/right
        self.rect.x += self.change_x

        # See if we hit the player
        hit = pygame.sprite.collide_rect(self, self.player)
        if hit:
            # We did hit the player. Shove the player around and
            # assume he/she won't hit anything else.

            # If we are moving right, set our right side
            # to the left side of the item we hit
            if self.change_x < 0:
                self.player.rect.right = self.rect.left
            else:
                # Otherwise if we are moving left, do the opposite.
                self.player.rect.left = self.rect.right

        # Move up/down
        self.rect.y += self.change_y

        # Check and see if we the player
        hit = pygame.sprite.collide_rect(self, self.player)
        if hit:
            # We did hit the player. Shove the player around and
            # assume he/she won't hit anything else.

            # Reset our position based on the top/bottom of the object.
            if self.change_y < 0:
                self.player.rect.bottom = self.rect.top
            else:
                self.player.rect.top = self.rect.bottom

        # Check the boundaries and see if we need to reverse
        # direction.
        if self.rect.bottom > self.boundary_bottom or self.rect.top < self.boundary_top:
            self.change_y *= -1

        cur_pos = self.rect.x - self.level.world_shift
        if cur_pos < self.boundary_left or cur_pos > self.boundary_right:
            self.change_x *= -1




wall = MovingEnemy(70,40)
wall.rect.x = 500
wall.rect.y = 400
wall.boundary_left = 250
wall.boundary_right = 800
wall.change_x = 1
walls.add(wall)

I am not sure if I have given the right information to receive help but I am honestly trying. I have browsed the internet for hours looking for a way to manage to do this and everything I try seems to not work. If anyone can understand this jumbled mess I have and help me out, I would really appreciate it.

Edit: I do have a player class, am I supposed to set the player within MovingEnemy to the class? I am not sure if that is possible or what exactly I am supposed to set it to. Here is my player class if this makes it easier.

class Player(pygame.sprite.Sprite):

    #Sets the starting speed
    change_x = 0
    change_y = 0
    walls = None


    def __init__(self, x, y):
        #creates the sprite for the player
        pygame.sprite.Sprite.__init__(self)

        #sets the size
        self.image = pygame.Surface([25,25])
        self.image.fill(green)

        self.rect = self.image.get_rect()
        self.rect.y = y
        self.rect.x = x

    def movement(self, x, y):

        self.change_x += x
        self.change_y += y

    def update(self):

        #changes the position of the player moving left and right
        self.rect.x += self.change_x



        #checks to see if the player sprite hits the wall
        collision = pygame.sprite.spritecollide(self, self.walls, False)
        for block in collision:
            # If the player hits a block while moving right, it is set back
            # to the left side of the block that was hit.
            if self.change_x > 0:
                self.rect.right = block.rect.left
            # Does the same as above, except with moving left.   
            else:
                self.rect.left = block.rect.right


        #changes the position of the player moving up and down    
        self.rect.y += self.change_y

        collision = pygame.sprite.spritecollide(self, self.walls, False)
        for block in collision:

            # Does the same as the above "for" except for moving up and down
            if self.change_y > 0:
                self.rect.bottom = block.rect.top
            else:
                self.rect.top = block.rect.bottom

Answer 1

In your MovingEnemy class you have an attribute called player . player 's starts out at None . No where in your code do you change player to anything but, None , hence player is of type none, or a NoneType . Nothing doesn't have the method rect which is used by the collide_rect method that you call.

Answer 2

Your compiler is telling you whats wrong.

walls.update()

First, your program calls walls.update, which is where the trouble begins.

hit = pygame.sprite.collide_rect(self, self.player)

Then, you try and detect hit detection between the wall and the player.

File "C:\Python34\lib\site-packages\pygame\sprite.py", line 1300, in collide_rect
return left.rect.colliderect(right.rect)

Notice the next clue comes in this line as this is ultimately the line that triggered the problem and it said this:

AttributeError: 'NoneType' object has no attribute 'rect'

Either your wall (self) or (self.player) is of type None, and thus has no attribute 'rect' with which it can determine a collision. Now note:

player = None

You never set player! Thus, player is of type None and has no attribute 'rect' to do collision detection.