int state=0;
int oldstate=0;

void setup(){
  pinMode(3,INPUT);
  Serial.begin(9600);
}


void loop(){
  state=digitalRead(3);

  if(state!=oldstate){
    if(state==HIGH){
      Serial.print(5, DEC);
    }
  }

  oldstate=state;
}


PYTHON




import os,serial
s=serial.Serial("/dev/tty.usbmodemfa141",9600)
while(1):
    if s.inWaiting() > 0:
        print s.read()