from django.contrib.auth import authenticate, login
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q
# 继承View 实现基于类的用户登陆
from django.views.generic.base import View 
from .models import UserProfile
# 重写 authenticate 登陆验证方法
class CustomBackend(ModelBackend):
  def authenticate(self, username=None, password=None, **kwargs):
    try:
     # 验证用户名或邮箱， Q提供了一个对象间的或（与&）运算
    user=UserProfile.objects.get(Q(username=username) | Q(email=username))
      # 后台密码为暗文，传入的密码为明文， 所以需要使用check_password()方法验证密码
      if user.check_password(password):
        # 验证成功返回user对象
        return user 
    # 登陆失败返回None
    except Exception as e:
      return None

# 基于类实现用户登陆
class LoginView(View):
  # 会根据 method 调用 post或者get方法
  def get(self, request):
    # 如果method为 GET 重新返回登陆页面
    return render(request, "login.html", {})

  def post(self, request):
    # 验证每个字段是否合法
    login_form = LoginForm(request.POST)
    # 对每个字段进行预处理，如果不合法，直接提示错误信息
    pre_check = login_form.is_valid()
    # 如果合法
    if pre_check:
      # 从POST中取出用户名和密码
      user_name = request.POST.get("username", "")
      if UserProfile.objects.filter(email=user_name):
        return render(request, "register.html", {"register_form": register_form, "msg": "用户已经存在"})
      pass_word = request.POST.get("password", "")
      # 此处为上面重写的authenticate方法
      user = authenticate(username=user_name, password=pass_word)
      if user is not None:   # 如果成功返回对象，失败返回None
        login(request, user) # 调用login方法登陆账号
        return render(request, "index.html")
      else:
        # 登陆失败
        return render(request, "login.html", {"msg":u"用户名或密码错误"})
    else:
      # form验证失败，给出错误信息
      return render(request, "login.html", {"login_form":login_form})

from django import forms
# 继承forms.Form
class LoginForm(forms.Form):
  # 如果为空则报错
  username = forms.CharField(required=True)
  # 同时也可以设定长度限制min_length、max_length
  password = forms.CharField(required=True, min_length=5)

<div class="form-group marb20 {% if login_form.errors.username %}errorput{% endif %}">

<div class="error btns login-form-tips" id="jsLoginTips">{% for key,error in login_form.errors.items %}{{ error }}{% endfor %} {{ msg }}</div>