simple ftdi-based DMX script in pthon

dmx.py

#!/usr/bin/python

import json
from ftdi import *
import math
import time

usleep = lambda x: time.sleep(x/1000000.0)

def start():
    ftdi_set_line_property2(c, BITS_8, STOP_BIT_2, NONE, BREAK_ON)
    usleep(100)
    ftdi_set_line_property2(c, BITS_8, STOP_BIT_2, NONE, BREAK_OFF)
    usleep(15)

def go(buf):
    start()
    ftdi_write_data(c,str(buf),len(buf))

c = ftdi_context()
ftdi_init(c)
ftdi_usb_open(c,0x0403,0x6001)
ftdi_set_baudrate(c,250000)
ftdi_setflowctrl(c,SIO_DISABLE_FLOW_CTRL)
ftdi_setrts(c,0)
ftdi_set_line_property(c, BITS_8, STOP_BIT_2, NONE)

buf = bytearray(513)

while True:
        json_data = open("/opt/spaceprobe/controller/api.json")
        data = json.load(json_data)
        json_data.close();

        if data["open"]:
                for i in range(8):
                        for j in range(3):
                                buf[1+j+i*3] = int(math.sin(
                                        time.time() +
                                        (j*2*math.pi/3) +
                                        2*math.pi*i/8
                                )*128+127)
        else:   
                for i in range(8*3):
                        buf[i+1] = 0

        go(buf)
        time.sleep(0.01)