Simple code to read AM2320 connected to Raspberry Pi in Python without external libraries

am2320.py

# AM2320 connected to Raspberry Pi pin 3 (SDA) and 5 (SCL)
# Public domain

import sys
import fcntl
import time
import struct

I2C_SLAVE = 0x0703
AM2320_ADDR = 0x5c

def crc_am2320(buf):
	crc = 0xffff

	for c in buf:
		if sys.version_info < (3, 0):
			crc ^= ord(c)
		else:
			crc ^= c
		for i in range(8):
			if crc & 1:
				crc >>= 1
				crc ^= 0xa001
			else:
				crc >>= 1

	return crc

def read_am2320(f, addr, count, tries=3):
	fcntl.ioctl(f.fileno(), I2C_SLAVE, AM2320_ADDR)

	buf = None

	while tries > 0:
		try:
			f.write(struct.pack("BBB", 3, addr, count))
			time.sleep(0.002)
			buf = f.read(4 + count)
			if len(buf) != 4 + count:
				raise IOError
			received_crc, = struct.unpack("<H", buf[-2:])
			if received_crc != crc_am2320(buf[:-2]):
				raise IOError
			return buf[2:-2]
		except IOError:
			buf = None
			time.sleep(0.002)
			tries -= 1
			continue

	return None

if len(sys.argv) != 2:
	print("usage: %s I2CDEVICE" % sys.argv[0])
	exit(1)

f = open(sys.argv[1], "rb+", 0)

buf = read_am2320(f, 0, 4)

if not buf:
	print("Unable to communicate")
	exit(1)

humid_tenths, temp_tenths = struct.unpack(">HH", buf)

print("t=%.1f rh=%.1f" % (temp_tenths / 10.0, humid_tenths / 10.0))