Bandpass filter for audio wav file
Consider looking at this StackOverflow answer which provides the full code for creating a Butterworth bandpass filter. In the sample code the answerer provides, the filter is applied to a manually constructed simplistic signal x. If you substitute this signal with your own NumPy array, it should achieve the intended effect.

WAV files can be quickly made into NumPy arrays, consider using the librosa module. librosa.core.load will be what you use. To write out the filtered signal, simply use librosa.output.write_wav.