how to not register user if they entered already registered password,email or username

 in views.py

in thsi example from form two password are taken to verify 

    you might be confused regarding message see message section blog post you will understand

def user_register(request):
    if request.method=="POST":
        fname= request.POST.get('firstname')
        lname= request.POST.get('lastname')
        username=request.POST.get('username')
        email=request.POST.get('email')
        pass1=request.POST.get('pass1')
        pass2=request.POST.get('pass2')
        if pass1!=pass2:
            messages.warning(request,'password does not match')
            return redirect('register')
        elif User.objects.filter(username=username).exists():
            messages.warning(request,'username already exists')
            return redirect('register')
        elif User.objects.filter(email=email).exists():
            messages.warning(request,'email already exists')
            return redirect('register')
        else:
            user=User.objects.create_user(first_name=fname,last_name=lname,username=username,email=email,password=pass1)
            user.save()
            messages.success(request,'user has been successfully registered')
            return redirect('login')