def get_particle_time_steps(particle_h5_file):
    """Get time steps stored in the HDF5 particle file

        Args :
            particle_h5_file : HDF5 file generated from particle tracking

        Returns :
            time_steps : list containing step numbers

        Raises :
            None
    """

    # read step numbers
    indices = particle_h5_file['Index']

    # add all keys to list, ignoring the 'Final' key
    time_steps = []
    for key in list(indices.keys()):
        if key != 'Final':
            time_steps.append(key)

    return time_steps