def parse_command_line_arguments():
    parser = argparse.ArgumentParser( description='Rotates the cell lattice in VASP POSCAR files' )
    parser.add_argument( 'poscar', help="filename of the VASP POSCAR to be processed" )
    parser.add_argument( '-a', '--axis', nargs=3, type=float, help="vector for rotation axis", required=True )
    parser.add_argument( '-d', '--degrees', type=int, help="rotation angle in degrees", required=True )
    args = parser.parse_args()
    return( args )