Python reading from serial

Question

I'm trying to read data from an RFID (RMD6300) to Raspberry Pi 1 in python but after reading for 30-40 secs whitout interruptions it crashes with the following error message:

Traceback (most recent call last): File "tmp.py", line 7, in string = ser.read(20) File "/usr/local/lib/python2.7/dist-packages/serial/serialposix.py", line 501, in read 'device reports readiness to read but returned no data ' serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)

this is my code:

import serial
ser = serial.Serial('/dev/ttyAMA0',9600, timeout=1)
IDs = ["xxxxxxxxxx","xxxxxxxxxx"]
while True:
 bool = False;
 string = ser.read(20)
 if len(string) == 0:
 print "Insert tag"
 continue
 else:
 for i in range(len(IDs)):
 for l in range(len(string)):
 if IDs[i] in string:
 print IDs[i]
 bool = True
 break
 else:
 string = string[1:]+string[0]
 if bool:
 break
 if not bool:
 print "Not found"

Answer 1

Question: ... device reports readiness to read but returned no data

Increase your timeout:

ser = serial.Serial('/dev/ttyAMA0',9600, timeout=1)

Use try ... except

try:
 string = ser.read(20)
except serial.serialutil.SerialException:
 except_counter +=1
 if except_counter == 5:
 break
 time.sleep(1)

Question: ...device disconnected or multiple access on port?

Can you exclude this two points?