I'm trying to get "three most recent 2000 constant-volume bars", is this code correct?

   for number in self.bond_price:
                vol_bar_one = self.Volume[0:2001]
                vol_bar_two = self.Volume[2001:4001]
                vol_bar_three = self.Volume[4001:6001]

                vol_bar_one_price = bond_price.vol_bar_one["close"]

                vol_bar_two_price = bond_price.vol_bar_two["close"]

                vol_bar_three_price = bond_price.vol_bar_three["close"]


My worry is that these bars will not remain static but will update with each new contract traded, kicking out the oldest value in the slice and inserting a new one for the "most recent value.