带阻Butterworth过滤器

我正在尝试使用python中的scipy库创建一个Bandstop Butterworth滤波器,您能告诉我我做错了吗? fc1是1750,fc2是4100,fs是30000,ft是150,我已经定义了它们。我的错误:ValueError:Wn必须为带通或带阻滤波器指定起始和终止频率。这是我到目前为止所拥有的代码:

fs = 33000 
r = 55
ft = 150
rp = 0.3
rs = 55
order = 3
a=1
fc1 = 1750
fc2 = 4100
fc=np.union1d(np.array([1,1750]),([4100,10000]))
wp = (fc1-ft/2) *2/fs

ws = (fc2 + ft/2) *2/fs

N, wn = sp.buttord(wp, ws, rp, rs)

b, a = sp.butter(N, wn , btype = "bandstop")

w,h = sp.freqz(b, a,  worN=512, plot=None)

f=(fs/2)*w/(np.pi)

plt.figure()

plt.plot(f,abs(h))