Arduino ultrasonic LED range graph thing (note this appends data, not renews it. It's a bug I might fix later)

graphingData.py

#!/usr/bin/env python

import serial, time
import pyqtgraph as pg
import pyqtgraph.multiprocess as mp


class Queue:
    """A sample implementation of a First-In-Never-Out
       data structure."""
    def __init__(self, length = 0):
        self.in_stack = []
        self.maxlen = length
    def __str__(self):
        return str(self.in_stack)
    def __repr__(self):
        return "<%s with %s>" % (self.__class__, self.in_stack)
    def push(self, obj):
        self.in_stack.append(obj)
        if self.maxlen != 0:
                if len(self.in_stack) > self.maxlen:
                        del self.in_stack[0]

    def get(self):
        return self.in_stack

if __name__ == "__main__":
        # Initialize the plot window
        pg.mkQApp()
        proc = mp.QtProcess()
        rpg = proc._import('pyqtgraph')
        plotwin = rpg.plot()
        curve = plotwin.plot(pen='y')
        plotwin.setDownsampling(auto=True)
        plotwin.setLabel('left', "distance", 'cm')
        plotwin.setLabel('bottom', "time")
        plotwin.enableAutoRange(False)
        data = proc.transfer([])
        q = Queue(15)

        s = serial.Serial('/dev/ttyACM0', 9600, timeout=1)

        while True:
                distance = s.readline().strip()
                if distance == '-1':
                        distance = 0
                q.push(int(distance))
                data.extend(q.get(), _callSync='off')
                curve.setData(y=data, _callSync='off')

LCDDistanceProject.ino

/*
 HC-SR04 Ping distance sensor:
 VCC to arduino 5v 
 GND to arduino GND
 Echo to Arduino pin 7 
 Trig to Arduino pin 8
 
 This sketch originates from Virtualmix: http://goo.gl/kJ8Gl
 Has been modified by Winkle ink here: http://winkleink.blogspot.com.au/2012/05/arduino-hc-sr04-ultrasonic-distance.html
 And modified further by ScottC here: http://arduinobasics.blogspot.com/
 on 10 Nov 2012.
 */


#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

#define echoPin 7 // Echo Pin
#define trigPin 8 // Trigger Pin
#define LEDPin 13 // Onboard LED

int maximumRange = 200; // Maximum range needed
int minimumRange = 0; // Minimum range needed
long duration, distance; // Duration used to calculate distance

void setup() {
 Serial.begin (9600);
 pinMode(trigPin, OUTPUT);
 pinMode(echoPin, INPUT);
 pinMode(LEDPin, OUTPUT); // Use LED indicator (if required)
 lcd.begin(16, 2);
 lcd.print("Distance (cm):");
}

void redraw()
{
  lcd.clear();
  lcd.print("Distance (cm):");
    // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
}

void loop() {
  // print the number of seconds since reset:
  //lcd.print(millis()/1000);
/* The following trigPin/echoPin cycle is used to determine the
 distance of the nearest object by bouncing soundwaves off of it. */ 
 digitalWrite(trigPin, LOW); 
 delayMicroseconds(2); 

 digitalWrite(trigPin, HIGH);
 delayMicroseconds(10); 
 
 digitalWrite(trigPin, LOW);
 duration = pulseIn(echoPin, HIGH);
 
 //Calculate the distance (in cm) based on the speed of sound.
 distance = duration/58.2;
 redraw();
 if (distance >= maximumRange || distance <= minimumRange){
 /* Send a negative number to computer and Turn LED ON 
 to indicate "out of range" */
 Serial.println("-1");
 lcd.print("(unknown)");
 digitalWrite(LEDPin, HIGH); 
 }
 else {
 /* Send the distance to the computer using Serial protocol, and
 turn LED OFF to indicate successful reading. */
 Serial.println(distance);
 lcd.print(distance);
 digitalWrite(LEDPin, LOW); 
 }
 
 //Delay 50ms before next reading.
 delay(50);
}