@staticmethod
def countParticles(shell, occupancy):
    'Count the number of particles (electrons) or quasiparticles\n        (holes) in a shell.'
    key = f'{shell}{occupancy}'
    if (key in ('s0', 's2', 'p0', 'p6', 'd0', 'd10', 'f0', 'f14')):
        particles = 'zero'
    elif (key in ('s1', 'p1', 'p5', 'd1', 'd9', 'f1', 'f13')):
        particles = 'one'
    else:
        particles = 'multiple'
    return particles
Count the number of particles (electrons) or quasiparticles
(holes) in a shell.
@staticmethod
def countParticles(shell, occupancy):
    'Count the number of particles (electrons) or quasiparticles\n        (holes) in a shell.'
    key = f'{shell}{occupancy}'
    if (key in ('s0', 's2', 'p0', 'p6', 'd0', 'd10', 'f0', 'f14')):
        particles = 'zero'
    elif (key in ('s1', 'p1', 'p5', 'd1', 'd9', 'f1', 'f13')):
        particles = 'one'
    else:
        particles = 'multiple'
    return particles