Python: 'NoneType' object is not subscript

Question

This question already has answers here:

Why do I get AttributeError: 'NoneType' object has no attribute 'something'? (10 answers)

Closed 6 months ago.

I'm new to databases in Python, so to practice some key skills I'm building a login screen that writes usernames and hashed passwords to the database, and then checks the user's inputs against what's in the database. However, when trying to pull the usernames and passwords from the database and storing them in variables, I keep getting the "'NoneType' object is not subscriptable" error.

How can I fix this?

This is the function from my program that contains the error

def login():
usernameAttempt = input("Enter your username: ")
passwordAttempt = input("Enter your password: ")

usernameSql = """SELECT Username FROM Details WHERE Password = '%s'""" % (passwordAttempt) # Selecting username in database
cur.execute(usernameSql)
usernameSql = cur.fetchone()
userFetched = usernameSql[0] # Pulling the item from the database

passwordSql = """SELECT Password FROM Details WHERE Username = '%s'""" % (usernameAttempt)
cur.execute(passwordSql)
passwordSql = cur.fetchone()
passFetched = passwordSql[0]

dbPassword, dbSalt = passFetched.split(":")

return dbPassword, dbSalt, passwordAttempt, usernameAttempt, userFetched, passFetched

I expected the variables userFetched and passFetched to be assigned the values held at indexes 0 in the username and password columns, but the error messages are as follows:

Traceback (most recent call last):

File "C:\Users\laure\Documents\Login screen.py", line 57, in dbPassword, dbSalt, passwordAttempt, usernameAttempt, userFetched, passFetched = login()

File "C:\Users\laure\Documents\Login screen.py", line 34, in login userFetched = usernameSql[0] # Pulling the item from the database TypeError: 'NoneType' object is not subscriptable

Answer 1

When tyour query return 0 rows fetchone will return None:

usernameSql = """SELECT Username FROM Details WHERE Password = '%s'""" % (passwordAttempt) # Selecting username in database
cur.execute(usernameSql)
usernameSql = cur.fetchone()
# check if the query return at least one record
if usernameSql:
    userFetched = usernameSql[0] 
else:
   # show a error or somthing

Answer 2

Your select Username query is returning no rows. So the result set is empty and there is nothing to fetch. So your fetchone call returns None instead of the row tuple you expect.