Pygame: Can someone help me implement double jumping?

I know there are already other posts about this out there, but my movement system is a little from the ones that I have found, so subsequently I am asking this question.

My movement system is based on a named tuple called Move(up,left,right,down) Then there is this:

def update(self, move, blocks):
    # check if we can jump 
    if move.up and self.on_ground:
        self.yvel -= self.jump_speed
    # simple left/right movement
    if move.left:
            self.xvel = -self.move_speed
    if move.right:
            self.xvel = self.move_speed

    # if in the air, fall down
    if not self.on_ground:
        self.yvel += 0.3
        # but not too fast
        if self.yvel > max_gravity: self.yvel = max_gravity

    # if no left/right movement, x speed is 0, of course
    if not (move.left or move.right):
        self.xvel = 0

    # move horizontal, and check for horizontal collisions
    self.rect.left += self.xvel
    self.collide(self.xvel, 0, blocks)

    # move vertically, and check for vertical collisions
    self.rect.top += self.yvel
    self.on_ground = False
    self.collide(0, self.yvel, blocks)

def collide(self, xvel, yvel, blocks):
    # all blocks that we collide with
    for block in [blocks[i] for i in self.rect.collidelistall(blocks)]:

        # if xvel is > 0, we know our right side bumped 
        # into the left side of a block etc.
        if xvel > 0:
                self.rect.right = block.rect.left;self.xvel=0
        if xvel < 0:
                self.rect.left = block.rect.right;self.xvel=0

        # if yvel > 0, we are falling, so if a collision happpens 
        # we know we hit the ground (remember, we seperated checking for
        # horizontal and vertical collision, so if yvel != 0, xvel is 0)
        if yvel > 0:
            self.rect.bottom = block.rect.top
            self.on_ground = True
            self.yvel = 0
        # if yvel < 0 and a collision occurs, we bumped our head
        # on a block above us
        if yvel < 0: self.rect.top = block.rect.bottom;self.yvel=0

I tried adding a fifth variable to the tuple called upUp, and when that was called it would trigger another jump, regardless of if on_ground was true or not.

To trigger it I used this in the event loop:

if e.type==KEYUP:
    if dj==0:
        dj=-1
    if dj=-1:
        dj='true'
Move(K_w,K_a,K_d,K_s,dj)

But this didn't work well at all! Anyone got any suggestions?