# Django 5.2.9 문서

# Writing views

A view function, or view for short, is a Python function that takes a web request and returns a web response. This response can be the HTML contents of a web page, or a redirect, or a 404 error, or an XML document, or an image … or anything, really. The view itself contains whatever arbitrary logic is necessary to return that response. This code can live anywhere you want, as long as it’s on your Python path. There’s no other requirement–no “magic,” so to speak. For the sake of putting the code somewhere, the convention is to put views in a file called `views.py`, placed in your project or application directory.

## A simple view

여기 현재 날짜와 시간을 HTML 문서로 반환하는 뷰가 있습니다:

    from django.http import HttpResponse
    import datetime

    def current_datetime(request):
        now = datetime.datetime.now()
        html = '<html lang="en"><body>It is now %s.</body></html>' % now
        return HttpResponse(html)

한 줄씩 이 코드를 밟아나가 봅시다.

- 첫 번째로, `django.http` 모듈로부터 `HttpResponse` 클래스를, 파이썬의 `datetime` 라이브러리와 함께 임포트합니다.

- 다음으로 `current_datetime` 라는 함수를 정의합니다. 이것이 뷰 함수입니다. 각각의 뷰 함수는 `HttpRequest` 객체를 첫 인자로 가지며, 이 객체는 일반적으로 ``request``라는 이름입니다.

  뷰 함수의 이름은 중요하지 않습니다. Django가 인식하도록 만들기 위해 특정한 방법으로 이름지을 필요는 없습니다. 여기서는 ``current_datetime``이라 부를 것이고, 이 이름이 하는 일을 분명하게 표현하기 때문입니다.

- 뷰는 생성된 응답을 담고 있는 `HttpResponse` 객체를 반환합니다. 각 뷰 함수는 `HttpResponse` 객체를 반환하는 역할을 합니다. (예외가 있지만, 나중에 알아보겠습니다)

Django’s Time Zone

Django는 ``America/Chicago``가 기본으로 설정되어 있는 `TIME_ZONE` 설정을 가지고 있습니다. 이 위치는 아마 여러분이 사시는 곳이 아니므로, 설정 파일에서 바꿀 수 있습니다.

## Mapping URLs to views

따라서 이 뷰 함수는 현재 날짜와 시간을 포함한 HTML 페이지를 반환합니다. 특정한 URL에 이 뷰를 표시하고 싶다면, *URLconf*를 만들어야 합니다. 자세한 내용은 URL dispatcher 를 참조하세요.

## 에러 반환

Django provides help for returning HTTP error codes. There are subclasses of `HttpResponse` for a number of common HTTP status codes other than 200 (which means “OK”). You can find the full list of available subclasses in the request/response documentation. Return an instance of one of those subclasses instead of a normal `HttpResponse` in order to signify an error. For example:

    from django.http import HttpResponse, HttpResponseNotFound

    def my_view(request):
        # ...
        if foo:
            return HttpResponseNotFound("<h1>Page not found</h1>")
        else:
            return HttpResponse("<h1>Page was found</h1>")

There isn’t a specialized subclass for every possible HTTP response code, since many of them aren’t going to be that common. However, as documented in the `HttpResponse` documentation, you can also pass the HTTP status code into the constructor for `HttpResponse` to create a return class for any status code you like. For example:

    from django.http import HttpResponse

    def my_view(request):
        # ...

        # Return a "created" (201) response code.
        return HttpResponse(status=201)

Because 404 errors are by far the most common HTTP error, there’s an easier way to handle those errors.

### The `Http404` exception

class django.http.Http404

When you return an error such as `HttpResponseNotFound`, you’re responsible for defining the HTML of the resulting error page:

    return HttpResponseNotFound("<h1>Page not found</h1>")

For convenience, and because it’s a good idea to have a consistent 404 error page across your site, Django provides an `Http404` exception. If you raise `Http404` at any point in a view function, Django will catch it and return the standard error page for your application, along with an HTTP error code 404.

예시 용례:

    from django.http import Http404
    from django.shortcuts import render
    from polls.models import Poll

    def detail(request, poll_id):
        try:
            p = Poll.objects.get(pk=poll_id)
        except Poll.DoesNotExist:
            raise Http404("Poll does not exist")
        return render(request, "polls/detail.html", {"poll": p})

In order to show customized HTML when Django returns a 404, you can create an HTML template named `404.html` and place it in the top level of your template tree. This template will then be served when `DEBUG` is set to `False`.

When `DEBUG` is `True`, you can provide a message to `Http404` and it will appear in the standard 404 debug template. Use these messages for debugging purposes; they generally aren’t suitable for use in a production 404 template.

## Customizing error views

The default error views in Django should suffice for most web applications, but can easily be overridden if you need any custom behavior. Specify the handlers as seen below in your URLconf (setting them anywhere else will have no effect).

The `page_not_found()` view is overridden by `handler404`:

    handler404 = "mysite.views.my_custom_page_not_found_view"

The `server_error()` view is overridden by `handler500`:

    handler500 = "mysite.views.my_custom_error_view"

The `permission_denied()` view is overridden by `handler403`:

    handler403 = "mysite.views.my_custom_permission_denied_view"

The `bad_request()` view is overridden by `handler400`:

    handler400 = "mysite.views.my_custom_bad_request_view"

더 보기

Use the `CSRF_FAILURE_VIEW` setting to override the CSRF error view.

### Testing custom error views

To test the response of a custom error handler, raise the appropriate exception in a test view. For example:

    from django.core.exceptions import PermissionDenied
    from django.http import HttpResponse
    from django.test import SimpleTestCase, override_settings
    from django.urls import path

    def response_error_handler(request, exception=None):
        return HttpResponse("Error handler content", status=403)

    def permission_denied_view(request):
        raise PermissionDenied

    urlpatterns = [
        path("403/", permission_denied_view),
    ]

    handler403 = response_error_handler

    # ROOT_URLCONF must specify the module that contains handler403 = ...
    @override_settings(ROOT_URLCONF=__name__)
    class CustomErrorHandlerTests(SimpleTestCase):
        def test_handler_renders_template_response(self):
            response = self.client.get("/403/")
            # Make assertions on the response here. For example:
            self.assertContains(response, "Error handler content", status_code=403)

## 비동기 뷰

As well as being synchronous functions, views can also be asynchronous (“async”) functions, normally defined using Python’s `async def` syntax. Django will automatically detect these and run them in an async context. However, you will need to use an async server based on ASGI to get their performance benefits.

Here’s an example of an async view:

    import datetime
    from django.http import HttpResponse

    async def current_datetime(request):
        now = datetime.datetime.now()
        html = '<html lang="en"><body>It is now %s.</body></html>' % now
        return HttpResponse(html)

You can read more about Django’s async support, and how to best use async views, in 비동기 지원.