Real Time FFT Filtering

I'm trying to use an old example code I found on the forums (attachment), but I can't plot the filtered fft signal correctly using the butter() passband filter from 400Hz to 2000Hz (10000Hz sampling rate and order doesn't matter). Also, I'd like to plot the audio signal in the time spectrum, with and without filtering. I've tried using ifft() to no avail, I'm guessing it has something to do with the way the plot updating works, any comments would be greatly appreciated!