I can't handle this Error TypeError: can't concat str to bytes

Question

import time import serial import sys SCREEN_DISPLAY=True SAVE_TO_FILE=True

txtfile = open('datafile.csv','rb')

serialport = serial.Serial('COM5',timeout=20,baudrate=9600)

while True:

sensordata = serialport.readline().decode('ascii')
timenow = time.strftime("Date: %Y-%m-%d // Time: %H:%M:%S // Temperature: ")

if SCREEN_DISPLAY: print(str.encode(timenow)+sensordata)
time.sleep(0.05)
if SAVE_TO_FILE: txtfile.write(str.encode(timenow)+sensordata)

serialport.close() txtfile.close()