ERROR in executing Python code contains mysql code gives error internalerror: unread result found

Hello This is my code for a school project
I've created two python files for this.
One is main.py and other one is book.py

While running my code it's showing me this error. It would be very helpful if you can solve my problem and give an effective solution.

Here's my code for book.py of function add_stock

def add_stock() :            
        print('Add Stock'.center(89 , '='))
        bno = unique_book_no()
        if bno :
            print("Book Number : " , bno)
        else : bno = int(input("Enter book number : "))
        bname = input("Enter the Book\'s Name : ")
        auth = input("Enter the Author of the Book : ")
        publ = input("Enter the Publisher of the Book : ")
        cost = eval(input("Enter the Cost per Book : "))
        stock = int(input("Enter the Quantity purchased : "))
        __cur.execute("insert into stock values ({} , '{}' , '{}' , '{}' , {} , {} , {} , '{}')".format(bno , bname , auth , publ , cost , stock , 0, __dt.date.today()))
        print("Inserted Successfully !!!")

And this one of book.py for function unique_book_no

def unique_book_no () :
        __cur.execute("select max(Book_No) from stock")
        data = __cur.fetchall(buffered=True)
        if bool(data[0][0]) :
            L1 = [x for x in range((data[0][0] + 1) , (data[0][0] + 10000))]
            shuffle(L1)
            return L1.pop(0)
        else : return False

I'm getting this error

Traceback (most recent call last):
      File "D:\CBSE 12\cs projects\Main.py", line 35, in <module>
        Book.add_stock()
      File "D:\CBSE 12\cs projects\Book.py", line 38, in add_stock
        bno = unique_book_no()
      File "D:\CBSE 12\cs projects\Book.py", line 90, in unique_book_no
        __cur.execute("select max(Book_No) from stock")
      File "C:\Python 37\lib\site-packages\mysql\connector\cursor.py", line 538, in execute
        self._connection.handle_unread_result()
      File "C:\Python 37\lib\site-packages\mysql\connector\connection.py", line 1455, in handle_unread_result
        raise errors.InternalError("Unread result found")
    mysql.connector.errors.InternalError: Unread result found