Raspberry and Arduino communication question!

import time
import picamera
import datetime
import requests
import os
from flask import Flask, redirect, url_for
from werkzeug import secure_filename
import serial


port = "/dev/ttyACM0"
serialFromArduino = serial.Serial(port, 9600)
serialFromArduino.flushInput()



while True:
    if(serialFromArduino.inWaiting() > 0):
        input = serialFromArduino.read(1)
#        #        input = serialFromArduino.read(1)
       # # print(input)
    if input=='a':
        with picamera.PiCamera() as camera:
                camera.brightness = 60
                camera.start_preview(fullscreen=False,window=(100,20,1024,768))
                time.sleep(5)
                camera.capture("A.jpg")
                print("AOK")
                camera.stop_preview()
                camera.close()
    if input=='b':
        with picamera.PiCamera() as camera:
                camera.brightness = 60
                camera.start_preview(fullscreen=False,window=(100,20,1024,768))
                time.sleep(5)
                camera.capture("B.jpg")
                print("BOK")
                camera.stop_preview()
                camera.close()

#include <Adafruit_Fingerprint.h>

#include <Wire.h>                            // I2C control library

#include <LiquidCrystal_I2C.h>          // LCD library 

#include <SoftwareSerial.h>

SoftwareSerial mySerial(18, 19);

#define SHOCK 5

LiquidCrystal_I2C lcd(0x27,16,2);



Adafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);

/////////////// switch////////////////////////////////////////

int inputPin = 2; // sensor signal pin

int pirState = LOW; // PIR initial state

int val = 0; // Signal Input



int RELAY=8;



/////////////// number of fingerprints/////////////////

int a=0;

//////////////////



void setup()  

{

Serial.begin(9600);

////////////////////////////////////////////////



 pinMode(A0,INPUT);

  pinMode(A1,INPUT);

  ////////////// shock detection//////////////

  pinMode(SHOCK, INPUT);





 ///////////////relay+electronic solenoid////////////

  pinMode(RELAY,OUTPUT);

 pinMode(3,OUTPUT);

 pinMode(4,OUTPUT);

  digitalWrite(RELAY,LOW); 





  /////////////////// power control switch/////////////////////////////////

 pinMode(inputPin, INPUT);



  ///////////////// fingerprint sensor//////////////////////////////////////////////////////// 

  while (!Serial);  // For Yun/Leo/Micro/Zero/...

  delay(100);

  Serial.println("\n\nAdafruit finger detect test");



  // // set the data rate for the sensor serial port

  finger.begin(57600);



  if (finger.verifyPassword()) {

    Serial.println("Found fingerprint sensor!");
  } 
  else {

    Serial.println("Did not find fingerprint sensor :(");
  }



  finger.getTemplateCount();

  Serial.print("Sensor contains "); Serial.print(finger.templateCount); Serial.println(" templates");

  Serial.println("Waiting for valid finger...");

  /////////////////////////////////////////////////////////////



}



void loop()                     // run over and over again

{

  ////////////// shock detection//////////////

  if (digitalRead(SHOCK ) == HIGH) 
  {

    Serial.println('b');

  }



  val = digitalRead(inputPin);

  ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////



  if(val == HIGH)

  {

  lcd.init();              

  lcd.setCursor(0,0);

  lcd.print("Welcome DDL!");

  lcd.setCursor(0,1);

  lcd.print("Put your finger!");

  lcd.backlight();

  Serial.println('a');



   /////////////// fingerprint sensor//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

   getFingerprintIDez();





    if(a>=0 && a<=2)

    {

      digitalWrite(3,LOW);

      digitalWrite(4,LOW);

    }   

  }



  else 

  {         
    Serial.println('c');

    lcd.noBacklight();  // turn on backlight  

    lcd.noDisplay();

  }



}

// // returns -1 if failed, otherwise returns ID #

int getFingerprintIDez() {

  digitalWrite(RELAY,LOW);

  uint8_t p = finger.getImage();

  if (p != FINGERPRINT_OK)  return -1;



  p = finger.image2Tz();

  if (p != FINGERPRINT_OK)  return -1;



  p = finger.fingerFastSearch();

  if (p != FINGERPRINT_OK) {

 a++;



 if(a>=3)

 {

  /////////EM Lock///////////////////////////

  digitalWrite(3,LOW);

  digitalWrite(4,HIGH);

///////////////////////////////////////////////////



  lcd.init();  

  lcd.setCursor(0,0);

  lcd.print("close the door");



  }



 lcd.init();  

 lcd.setCursor(0,0);

 lcd.print("Unsaved        ");

 lcd.setCursor(0,1);

 lcd.print("Fingerprint     ");

  return -1;

  }

  //If you get the fingerprint wrong//



  a=0;//number of times wrong



  lcd.init();  

  lcd.setCursor(0,0);

  lcd.print("Open the door");

  delay(100);

  lcd.setCursor(0,1);

  lcd.print("                ");

  delay(100);

  lcd.setCursor(0,0);

  lcd.print("Welcome DDL!   ");

  lcd.setCursor(0,1);

  lcd.print("Put your finger!");

  // // found a match!

  Serial.print("Found ID #"); Serial.print(finger.fingerID); 

  Serial.print(" with confidence of "); Serial.println(finger.confidence);

   digitalWrite(RELAY,HIGH);

  delay(300);

  return finger.fingerID; 

}