The major train stations in Paris have lockers and/or “left luggage” rooms where you can leave your bag.  However, because of security concerns, some places are shutting down, others have fairly short time limits on how long you can leave a bag.  Some of the facilites now require airline-type luggage screening.  Since the equipment and staffing are expensive, it can be very expensive to stow a bag.  I’d count on 5 euros per bag per day.

http://en.parisinfo….