Read serial data from multiple arduino

Question

Please help me find problem in this code:

import serial
ser=serial.Serial("/dev/ttyACM0",9600)
ser.baudrate=9600
ser1=serial.Serial("/dev/ttyUSB0",9600)
ser1.baudrate=9600
ser2=serial.Serial("/dev/ttyUSB1",9600)
ser2.baudrate=9600

while True: 

 read_ser=ser.readline()
 read_ser1=ser1.readline()
 read_ser1=ser2.readline()
 print(read_ser)
 print(read_ser1)
 print(read_ser2)

I expect that it will show me message from connected Arduino. Arduino send it when I apply card to RFID reader. But, it send only from first ser

Update:

I connect 3 Arduino Uno to Raspberry Pi 3 via USB. Each Arduino connect with RFID-RC522.

ls -l /dev/ttyACM*  
crw-rw---- 1 root dialout 166, 0 Oct 18 19:17 /dev/ttyACM0

But Arduinos connect to /dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyACM0

Answer 1

This code works as I expected

import serial
ser=serial.Serial("/dev/ttyACM0",9600,timeout=1)
ser.baudrate=9600
ser1=serial.Serial("/dev/ttyUSB0",9600,timeout=1)
ser1.baudrate=9600
ser2=serial.Serial("/dev/ttyUSB1",9600,timeout=1)
ser2.baudrate=9600
while True: # Run forever

 read_ser=ser.readline()
 if (read_ser != ""):
        print(read_ser)
 read_ser1=ser1.readline()
 if (read_ser1 != ""):
         print(read_ser1)
 read_ser2=ser2.readline()
 if (read_ser2 != ""):
         print(read_ser2)

Thank you @jasonharper