got exception when do a loop input to database Python

Question

So, I want to input data in multiple times with auto increment as primary key and return the primary key as the input result. so there's my code:

connectDB.py

import pymysql
class auth:

   db = pymysql.connect("localhost","root","","rfid")

   cursor = db.cursor()

   def inputData(nama):
       sql = "INSERT INTO auth (nama) VALUES ('%s');" % (nama)

       try:
           auth.cursor.execute(sql)
           auth.db.commit()


           result = auth.cursor.lastrowid

           auth.db.close()

           return result
       except:
           err = "Error: unable to fetch data"
           auth.db.rollback()

           auth.db.close()

           return err

test.py

import re
import PyMySQL
from connectDB import auth

while True:

     inputs2 = input("masukan nama: ")


     hasil = auth.inputData(inputs2)

     print(hasil)

so, when I do an input in the first time is success but when Itry to input again I got an error exception:

Traceback (most recent call last):
  File "/home/pi/Desktop/learn/RFIDdatabase/connectDB.py", line 29, in inputData
auth.cursor.execute(sql)

  File "/usr/local/lib/python3.4/dist-packages/pymysql/cursors.py", line 166, in execute
result = self._query(query)

  File "/usr/local/lib/python3.4/dist-packages/pymysql/cursors.py", line 322, in _query
conn.query(q)

  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 855, in query
self._execute_command(COMMAND.COM_QUERY, sql)

  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 1071, in _execute_command
raise err.InterfaceError("(0, '')") 
pymysql.err.InterfaceError: (0, '')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 12, in <module>
hasil = auth.inputData(inputs2)

  File "/home/pi/Desktop/learn/RFIDdatabase/connectDB.py", line 41, in inputData
auth.db.rollback()

  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 792, in rollback
self._execute_command(COMMAND.COM_QUERY, "ROLLBACK")

  File "/usr/local/lib/python3.4/dist-packages/pymysql/connections.py", line 1071, in _execute_command
raise err.InterfaceError("(0, '')")
pymysql.err.InterfaceError: (0, '')

so, What the exception cause?

Answer 1

Of course you would get an exception - cause you close the connection after executing a query:

auth.cursor.execute(sql)
auth.db.commit()

result = auth.cursor.lastrowid

auth.db.close()  # < HERE

return result

You probably getting an "operation on a closed cursor" exception which is handled by your overly broad bare except clause (which is bad) - then - the roll back is initiated at auth.db.rollback() which fails with a not descriptive and understandable error.

Other issues:

• I would make the db and cursor instance variables instead of class variables (differences)
• don't "string format" your queries - proper parameterize them