Code that for some reason causes Arduino to crash

#!/usr/bin/env python3.6
# Trying this serial  wont work  and causes  arduino to  lock #
# Bryan  Cairns   Void Realms Face  Book #

#MD Harrington

import mariadb
import serial
import syslog
import time
import threading



port='/dev/ttyACM0'
baudrate=57600
ser = serial.Serial(port,baudrate,timeout=5)
global conn

def activatePort():
    m_text="Hello world"
    m_arr=m_text.encode('ansii')
    ser.write(m_arr)
    sleep(20)
    ser.close()
    print("Finished")





def doSql(ID):
        # Connect to MariaDB Platform
    try:
        conn = mariadb.connect(
            user="xxxx",
            password="xxxxx",
            host="192.168.0.80",
            port=3306,
            database="Instructions"

        )
        cursor = conn.cursor()
        statement = "SELECT ID, Username , Message FROM Instructions.Messages WHERE ID=%s"
        data = (ID,)
        print(f"Messages For ID = {ID} ")
        cursor.execute(statement, data)
        row = cursor.fetchone()
        while row:
            name = row[1]
            print (name)
            msg= row[2]
            print (msg)

            row = cursor.fetchone()
        conn.close()


    except mariadb.Error as e:
        print(f"Error retrieving entry from database: {e}")



ID ="MDWONE"

# tried  with threading as welland without

x =threading.Thread(target=activatePort)
x.start()

y= threading.Thread(target=doSql,args=(ID,))
y.start()

ser.close()
exit(1)