Python 2 to Python 3 Struct Issue

[robin73]

I'm trying to get the following code to work in Python 3. It is fine in Python 2. I have changed the xranges to range, but there is a problem with this line: data = ''.join(struct.pack('f', samp) for samp in tone):

Error:
sequence item 0: expected str instance, bytes found.

I found this answer but couldn't work out how to apply it to my situation. Any help much appreciated.

    import math
    import struct
    import pyaudio

    def play_tone(frequency, amplitude, duration, fs, stream):
        N = int(fs / frequency)
        T = int(frequency * duration)  # repeat for T cycles
        dt = 1.0 / fs
        # 1 cycle
        tone = (amplitude * math.sin(2 * math.pi * frequency * n * dt)
                for n in xrange(N))
        # todo: get the format from the stream; this assumes Float32
        data = ''.join(struct.pack('f', samp) for samp in tone)
        for n in xrange(T):
            stream.write(data)

    fs = 48000
    p = pyaudio.PyAudio()
    stream = p.open(
        format=pyaudio.paFloat32,
        channels=1,
        rate=fs,
        output=True)

    # play the C major scale
    scale = [130.8, 146.8, 164.8, 174.6, 195.0, 220.0, 246.9, 261.6]
    for tone in scale:
        play_tone(tone, 0.5, 0.75, fs, stream)

    # up an octave
    for tone in scale[1:]:
        play_tone(2*tone, 0.5, 0.75, fs, stream)

    stream.close()
    p.terminate()