即使行在数据库中，Python mySQL.connector 也返回 None

Question

I'm making a server application where when a client connects, it determines whether it can send data or just listen to incoming data. It determines if it is a "sending" client via the following code:

try:
    conn = mysql.connector.connect(host=config['databaseHost'], user=config['databaseUser'], password=config['databasePassword'], port=config['databasePort'])

except mysql.connector.Error as err:
    print(err)

cur = conn.cursor()
cur.execute("USE tcpPractice")
cur.execute("SELECT ip_address FROM client_list")
res = cur.fetchall()

for item in res:
    if item[0] not in senders:
        senders.append(item[0])

In the above code, if the address of the client is not in the list generated by res, it continues to the second part of the code, which is to determine if it is a listening client. Here, clients that can listen are authenticated by username and password. Here, I query the database for the given username and grab the password associated with it. However, when I run the below code to do so:

socket.send("Enter your username: ".encode())
username = socket.recv(SIZE).decode()
socket.send("Enter your password: ".encode())
password = socket.recv(SIZE).decode()


statement = "SELECT passwd FROM users_table WHERE username = %s"

try:
    cur.execute(statement, (username, ))
except mysql.connector.Error as err:
    print(err)

hashed = cur.fetchone()

hashed always returns None, even when I test using a username and password that I know is in the database. I tried closing the connection and cursor and recreating them to no avail, I made sure that syntax is correct, I made sure that I am using the correct database, I made sure that I am querying the correct table and looking for the correct column, I tried commiting after every execute statement, but nothing so far has worked.

As a test, I tried the above in the Python shell (minus the lines related to the socket) and it works as intended there. I tried searching for this issue, but none of the solutions I looked at worked. Any ideas what the issue might be?

EDIT: Forgot to mention that I am using netcat to connect to the server application, I'm not using any custom client program.

EDIT2: I just found that hardcoding the username like so:

statement = "SELECT passwd FROM users_table WHERE username = 'testUser'"
cur.execute(statement)

works as intended and hashed no longer returns None, so I'm pretty sure the problem lies in either the prepared statement I'm trying to use or how I'm receiving the username from the client.

EDIT3: I figured out what the issue was, I posted what the solution was.

Answer 1

I found out what the issue was. As it turns out, all the inputs from netcat had a \\n at the end of them, which was making the query fail. So, doing this:

socket.send("Enter your username: ".encode())
username = socket.recv(SIZE).decode().strip()
socket.send("Enter your password: ".encode())
password = socket.recv(SIZE).decode().strip()

fixed the issue and the server is now working as intended.

Answer 2

change the statement to statement = "SELECT passwd FROM users_table WHERE username = '%s'"

Is it missing the quotes?