import wave
import numpy as np

def save_wav_channel(fn, wav, channel):
    '''
    Take Wave_read object as an input and save one of its
    channels into a separate .wav file.
    '''
    # Read data
    nch   = wav.getnchannels()
    depth = wav.getsampwidth()
    wav.setpos(0)
    sdata = wav.readframes(wav.getnframes())

    # Extract channel data (24-bit data not supported)
    typ = { 1: np.uint8, 2: np.uint16, 4: np.uint32 }.get(depth)
    if not typ:
        raise ValueError("sample width {} not supported".format(depth))
    if channel >= nch:
        raise ValueError("cannot extract channel {} out of {}".format(channel+1, nch))
    print ("Extracting channel {} out of {} channels, {}-bit depth".format(channel+1, nch, depth*8))
    data = np.fromstring(sdata, dtype=typ)
    ch_data = data[channel::nch]

    # Save channel to a separate file
    outwav = wave.open(fn, 'w')
    outwav.setparams(wav.getparams())
    outwav.setnchannels(1)
    outwav.writeframes(ch_data.tostring())
    outwav.close()

wav = wave.open(WAV_FILENAME)
save_wav_channel('ch1.wav', wav, 0)
save_wav_channel('ch2.wav', wav, 1)