IntegrityError at /incibup唯一约束失败：auth_user.username ---＆gt;在Django

Question

当我单击登录按钮时，我会收到完整性错误！我已经在管理站点上签到了，所有用户都可以正确地看到我已注册。但是，当我单击登录按钮，其中已在管理员中注册的条目时，我的代码崩溃并给出完整性错误！

Views.py：

from django.http import HttpResponse
from django.shortcuts import redirect, render , HttpResponse
from django.contrib.auth.models import User
from django.contrib import messages
from django.contrib.auth import authenticate , login




# Create your views here.
def home(request):
    return render(request,"authentication/index.html")
def signup(request):
    if request.method=="POST": 
        username=request.POST.get('username')
        fname=request.POST.get('fname')
        lname=request.POST.get('lname')
        email=request.POST.get('email')
        pass1=request.POST.get('pass1')
        pass2=request.POST.get('pass2')
        myuser=User.objects.create_user(username,email,pass1) #creating user
        myuser.first_name=fname
        myuser.last_name=lname
        myuser.save() 
        messages.success(request,"Your account has been successfuly created")
        return redirect('/signin')


    return render(request,"authentication/signup.html")

def signin(request):
    if request.method=='POST':
        username=request.POST.get('username')
        pass1=request.POST.get('pass1')
        user=authenticate(username=username,password=pass1) 
        if user is not None: 
            login(request,user)
           
            return render(request,"authentication/index.html")
        else:
            messages.error(request,"Bad credentials") 
            redirect('home')


    return render(request,"authentication/signin.html")
def signout(request):
    pass