def tra_number_atoms(snapshots):
    """
    Get atom number, time and iteration from multiple snapshots.

    Args:
        snapshots (list[:class:`.Snap`]): snapshots the atomic information

    Returns:
        (tuple): tuple containing:

            - list[int]: number of atoms in each snapshot
            - list[float]: time in simulation of the snapshots
            - list[int]: iteration in simulation of the snapshots
    """
    atoms = []
    times = []
    iterations = []
    # loop through snapshots and save information to list
    for i in range(len(snapshots)):
        atoms.append(len(snapshots[i].atoms))
        times.append(snapshots[i].time)
        iterations.append(snapshots[i].iter)
    return atoms, times, iterations