我该如何解决： TypeError: 'NoneType' object is not iterable

Question

I have a Python Flask code and here is this error for me: TypeError: 'NoneType' object is not iterable. Thus, in the app there are two types of sessions: pro and common, if the user's email is in the db pro list it will be redirected to a screen, otherwise it will be redirected to it.

    ###########################
    conn = mysql.connector.connect(host="localhost",
                              database="*********", user="root",
                              password="********")

    ku = conn.cursor()

    em = ku.execute("SELECT Email FROM pro WHERE email=%s",(emails,))
    emm = ku.fetchone()
    
    
    nms2 = [str(i) for i in emm]
    emai = str("".join(nms2))
    

    ###########################
    if resposta:
        session["loggedin"] = True
        session["email"] = resposta[1]
        if emails in emai:
            return redirect(url_for("home_pro"))
        
        return redirect(url_for("home"))
    else:
        msg="Email/Senha incorretos"

    ###########################

How can I resolve this error? In Python, the error is on the line: nms2 = [str(i) for i in emm]

Answer 1

Check if the emm is empty/None before running a for loop on it.

Answer 2

fetchone() method gives the row if required row exist in database. there is no row in database where your condition is matched. You can handle this error like this:

if emm is not None:
    nms2 = [str(i) for i in emm]
    emai = str("".join(nms2))
else:
    print("No row found with that email")