Raspberry Pi SPI input from MCP3008 IC

#!sudo /usr/bin/python

import signal
import sys
import spidev
import time


def signal_handler(signal, frame):
    print 'Cleaning up...'
    sys.exit(0)


# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum):
    if ((adcnum > 7) or (adcnum < 0)):
            return -1
    r = spi.xfer2([1, (8 + adcnum) << 4, 0])
    adcout = ((r[1] & 3) << 8) + r[2]
    return adcout


signal.signal(signal.SIGINT, signal_handler)

DEBUG = 1

spi = spidev.SpiDev()
spi.open(0, 0)

print "Max Speed: %d" % spi.max_speed_hz
print "Bit per word: %d" % spi.bits_per_word

# Microphone analog output connected to channel 4 of mcp3008
adcnum = 4
sleep_time = 0.05

while True:
    read_adc0 = readadc(adcnum)
    psense = read_adc0 * (3.3 / 1024.0)

    if DEBUG:
        #print "%.2f" % (read_adc0)
        print "psense: %.2f" % psense

    time.sleep(sleep_time)