在html页面中填写注册表单后，它会出现此错误并使用用户名和密码并以登录表单存储值

在html页面中填写注册表单后，它会出现此错误并使用用户名和密码以及以登录形式存储值：

TypeError at /login/ argument of type 'NoneType' is not iterable.

models.py:

from django.db import models
from django.utils.translation import ugettext_lazy as _

class signup(models.Model):
    email = models.EmailField();
    full_name = models.CharField(max_length=120)
    username = models.CharField(_('username'), max_length=20, primary_key = True)
    department= models.CharField(max_length=20)
    password = models.CharField(_('password'), max_length=128)
    pic=models.ImageField(upload_to=None, height_field=None, width_field=None, max_length=100, default='default.png')
    created= models.DateTimeField(auto_now_add=True, auto_now=False)
    updated= models.DateTimeField(auto_now_add=False, auto_now=True)

    def __str__(self):
        return self.username

class login(models.Model):
    username = models.CharField(_('username'), max_length=20)
    password = models.CharField(_('password'), max_length=128)
    login= models.DateTimeField(_('last_login'),auto_now_add=False, auto_now=True)

    def __str__(self):
        return self.username

forms.py:

from django import forms
from .models import signup
from .models import login

class loginForm(forms.ModelForm):
    password=forms.CharField(widget=forms.PasswordInput())
    class Meta:
            model=login
            fields=['username','password']


class SignUpForm(forms.ModelForm):
    password=forms.CharField(widget=forms.PasswordInput())
    class Meta:
            model=signup
            fields=['username','full_name', 'email','department','password','pic']

views.py:

from django.shortcuts import render
from .forms import  SignUpForm
from .forms import  loginForm
from django.db import connection

def home(request):
    title= 'welcome'
    form = SignUpForm(data = request.POST or None)
    print(form.is_valid)
    if form.is_valid():
        instance = form.save(commit=False)
        instance.save()
        print(instance)
        print(instance.email)
    context = {
        "title": title,
        "form": form,           
    }       
    return render(request,"base.html", context)

def login(request):
    form = loginForm(data = request.POST or None)
    if form.is_valid():
        instance = form.save(commit=False)

        username=instance.username
        password=instance.password
        row=auth(username,password)
        if password in row:
            instance.save()
            form1=SignUpForm
            context={
                "form":form1,
                "instance":instance
            }
            return render(request, "profile.html", context)
    title= 'welcome back'
    context ={
        "title":title,
        "form":form    
    }       
    return render(request, "login.html", context)

def auth(username,password):
    cursor = connection.cursor()
    cursor.execute("SELECT password FROM teacher_signup WHERE username = %s", [username])
    row = cursor.fetchone()    
    return row

当点击注册按钮[如果行中的密码：]以某种方式调用此行 .