https://docs.djangoproject.com/en/3.0/topics/http/views/#customizing-error-views

# urls.py

from Blog.views import HomeView, ErrorView, ErrorView2

...
# 방법1
handler400 = ErrorView.as_view()
handler403 = ErrorView.as_view()
handler404 = ErrorView.as_view()
handler500 = ErrorView.as_view()

# 방법2
handler400 = ErrorView2.viewPage
handler403 = ErrorView2.viewPage
handler404 = ErrorView2.viewPage
handler500 = ErrorView2.viewPage

# views.py

from django.views.generic.base import TemplateView
from django.http import request
from django.http.response import HttpResponse
from django.shortcuts import render_to_response, render
from django.template import loader
from django.template.context import RequestContext

class ErrorView(TemplateView):
    template_name = "error/error.html"
    
    def get_context_data(self, **kwargs):
        context = TemplateView.get_context_data(self, **kwargs)
        context["error_code"] = 404
        return context


class ErrorView2():
    @classmethod
    def viewPage(cls, request, exception=None):
        #return HttpResponse("Error!!", status=404)
        
        #=======================================================================
        # response = HttpResponse()
        # response.write("hello!</br>")
        # response.write("page not found")
        # response["error_code"] = 404
        # return response
        #=======================================================================
        
        #t = loader.get_template("error/error.html")
        #return HttpResponse(t.render({"error_code":"404"}, request))
        
        return render(request, "error/error.html", {"error_code":"404", "exception":exception}, status=404)
        
        # deprecated
        #return render_to_response("error/error.html", {"error_code":"404"}, RequestContext(request), status=404)
        #return render_to_response("error/error.html", {"error_code":"404"}, RequestContext(request))
        #return render_to_response('error/error.html', {"error_code":"404"})

# /templates/error/error.html

{% extends "default.html" %}

{% block title %}Raise error{% endblock title %}

{% block content %}
{{ error_cdoe }}
{% endblock content %}