arduino.py

import pyaudio
import audioop
import serial

CHUNK = 1024
FORMAT = pyaudio.paInt16
CHANNELS = 2
RATE = 44100
RECORD_SECONDS = 5

arduino = serial.Serial('/dev/ttyUSB0')
p = pyaudio.PyAudio()

stream = p.open(
    format=FORMAT,
    channels=CHANNELS,
    rate=RATE,
    input=True,
    frames_per_buffer=CHUNK
)

for i in range(0, int(RATE / CHUNK * RECORD_SECONDS)):
    data = stream.read(CHUNK)
    rms = audioop.rms(data, 2)    # here's where you calculate the volume
    arduino.write(rms)
    print(rms)

stream.stop_stream()
stream.close()
p.terminate()
arduino.close()