Pull data from markitondemand and send it to my arduino's LCD screen that sits above my dining room table.

get-markit-data.py

import time
import math
import urllib2
import json
import traceback

ser = None
MARKIT_PAUSE = 3
#MOUNT = "/dev/ttyACM0" #raspi
MOUNT = "COM3" #windows
URL_BASE = "http://dev.markitondemand.com/Api/v2/Quote/json"
SYMBOLS_1 = ["AAPL" , "MSFT", "NFLX"]
SYMBOLS_2 = ["JNJ", "GE", "KR"]
SYMBOLS_3 = ["CTAS", "BP", "CVX"]
SYMBOLS_4 = ["SCTY", "FB", "AMZN"]

SYMBOLS_A = [SYMBOLS_1, SYMBOLS_2, SYMBOLS_3, SYMBOLS_4]


SOCKET_ON = True

if SOCKET_ON:
    import serial
    ser = serial.Serial(MOUNT, 9600)
        
def send( a_string ):
    global ser
    # Markit gives some unicode but we dont actually need it
    a_string = a_string.encode('ascii','ignore')
    print a_string
    if SOCKET_ON:
        ser.write(a_string)

def sendLine(line, val):
    print "Sending line " + line + ", " + val
    tosend = line + ":" + val
    if(len(tosend) > 64):
        print "WARNING: string will be cut off by serial bufffer (64 bytes)"
    send(tosend)
    
def getMarkitData(symbols):
    quotes = []
    for s in symbols:
        url = URL_BASE + "?symbol=" + s
        print "Query URL: " + url
        req = urllib2.Request(url)
        response = urllib2.urlopen(req)
        quotes.append(json.loads(response.read()))
        # Don't hit their API super hard, they have a req/sec limit
        time.sleep(MARKIT_PAUSE)
    return quotes
        
def processMarkitData(data):
    quote_strings = ""
    for quote in data:
        #print quote
        if not "Symbol" in quote:
            continue
        quote_strings += quote["Symbol"] + ":" + \
            str(round(quote["LastPrice"], 2)) + \
            ", " + str(round(quote["ChangePercent"], 2)) + "% "
    return quote_strings

def sendSymbols(symbols, line):
    data = getMarkitData(symbols)
    strings = processMarkitData(data)
    sendLine(line, strings)

"""
Give it a second or two between sending lines, otherwise it will interpret them 
as the same line. Easier to wait, than programming in line split chars 
and a method to do that on the board. 
"""
def doUpdate():    
    time.sleep(2)    
    try:
        i = 0
        for s in SYMBOLS_A:
            i += 1
            sendSymbols(s, str(i))
            time.sleep(3)

    except Exception, e:
        print str(e)
        print(traceback.format_exc())
        time.sleep(2)
        sendLine("4", str(e))

if __name__ == "__main__":
    doUpdate()

lcd-controller.ino

#include <LiquidCrystal_SR3W.h>
#include <LiquidCrystal_SR2W.h>
#include <FastIO.h>
#include <LiquidCrystal.h>
#include <String.h>
#include <LCD.h>
#include <I2CIO.h>
#include <LiquidCrystal_I2C.h>
#include <LiquidCrystal_SR.h>
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>


/*
** Example Arduino sketch for SainSmart I2C LCD2004 adapter for HD44780 LCD screens
** Readily found on eBay or http://www.sainsmart.com/ 
** The LCD2004 module appears to be identical to one marketed by YwRobot
**
** Address pins 0,1 & 2 are all permenantly tied high so the address is fixed at 0x27
**
** Written for and tested with Arduino 1.0
** This example uses F Malpartida's NewLiquidCrystal library. Obtain from:
** https://bitbucket.org/fmalpartida/new-liquidcrystal 
**
** Edward Comer
** LICENSE: GNU General Public License, version 3 (GPL-3.0)
**
** NOTE: TEsted on Arduino NANO whose I2C pins are A4==SDA, A5==SCL
* 
* 10/2/2015 - ard
*   NOTE: remove the included ardiuno library called "LiquidCrystal" and include the NewLiquidCrystal library (I used tag 'V 1.3.1')
*     https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
* 
*   Also, don't re-order the imports, they need to go in this order
* 
* 
*/

#define I2C_ADDR    0x27  // Define I2C Address where the PCF8574A is
#define BACKLIGHT_PIN     3
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7

LiquidCrystal_I2C       lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

// led controller:
int num_leds = 10;
int led10 = 13;
int led9 = 12;
int led8 = 11;
int led7 = 10;
int led6 = 9;
int led5 = 8;
int led4 = 7;
int led3 = 6;
int led2 = 5;
int led1 = 4;
int led_side_light = 2;

int led_indicator_array[] = { 
  led10, 
  led9, 
  led8, 
  led7,
  led6,
  led5,
  led4,
  led3,
  led2,
  led1
};

void setup()
{
  // init lcd screen
  lcdInit();
  // init leds:
  initLedPins();
  // init serial cxn.
  sendSerialDataInit();
}

void lcdInit(){
  lcd.begin (20,4);
  // Switch on the backlight
  lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
  lcd.setBacklight(HIGH);
  lcd.home ();   
}

void initLedPins(){
  for( int i=0; i < sizeof(led_indicator_array); i++) {
    pinMode( led_indicator_array[i], OUTPUT);
    digitalWrite( led_indicator_array[i], LOW);
  }
  
  pinMode( led_side_light, OUTPUT);
  digitalWrite( led_side_light, LOW);
}

void sendSerialDataInit(){
  Serial.begin(9600);
  Serial.println("\nThe LCD is on, serial listening for data.");
}

String getLine( String input_str, int iter, int width){
  int len_str = input_str.length();
  // e.g. 34983 % 50 
  int mod = iter % len_str; // n can be up max integer
  
  int position_start = mod;
  int position_end = mod + width;
  //Serial.println("start " + position_start);
  //Serial.println("end " + position_end);
  // case short string
  if( len_str <= width ) {
    return input_str;
  }
  
  // case @ end of string- get some of the first part of the string also.
  if(position_end > len_str) {
    String toDisplay = input_str.substring(position_start, input_str.length()) + input_str.substring(0, position_end - len_str);
    return toDisplay;  
  }
  
  // case @ medium
  return input_str.substring( position_start, position_end);
}

// other misc globals:
int n = 0;

// Pull strings off of serial and read-em!
String line1 = "no data .";
String line2 = ".:--:_=|-_-^-_-^-_-^-_-^-_-^-___-^-()_";
String line3 = "no data ...";
String line4 = "no data ...";


void setLine(String content){
  if(content.substring(0, 2) == "1:"){
    line1 = content.substring(2, content.length());
    Serial.println("Line 1: " + line1);
  } else if(content.substring(0, 2) == "2:"){
    line2 = content.substring(2, content.length());
    Serial.println("Line 2: " + line2);
  } else if(content.substring(0, 2) == "3:"){
    line3 = content.substring(2, content.length());
    Serial.println("Line 3: " + line3);
  } else if(content.substring(0, 2) == "4:"){
    line4 = content.substring(2, content.length());
    Serial.println("Line 4: " + line4);
  }
}

void readSerialAndSetLine(){
  String content = "";
  char character;

  while(Serial.available()) {
      character = Serial.read();
      content.concat(character);
  }
  // send it back to be sure:
  if (content != "") {
    Serial.println(content);
  }
  setLine(content);
}


void loop()
{
  readSerialAndSetLine();
  if(n <= 0) n = 0; // not a uint
  lcd.setCursor ( 0, 0 );
  lcd.print(getLine(line1, n, 20));  
  lcd.setCursor ( 0, 1 );        // go to the 2nd line
  lcd.print(getLine(line2, n, 20));
  lcd.setCursor ( 0, 2 );        // go to the third line
  lcd.print(getLine(line3, n, 20));
  lcd.setCursor ( 0, 3 );        // go to the fourth line
  lcd.print(getLine(line4, n, 20));
  
  // example:
  //lcd.setCursor (14,3);        // go col 14 of line 3
  //lcd.print(n++,DEC);
  
  Serial.println("\n Iteration: " + (String)n);
  
  //lcd.setBacklight(HIGH);     // Backlight on
  delay(1500);
  n++;
  
}