How to use the starlette.responses.PlainTextResponse function in starlette

async def __call__(self, scope, receive, send):
            response = PlainTextResponse("OK")
            await response(scope, receive, send)

def foo(request):
            return PlainTextResponse("Foo")

async def test_get_from_cache_head(cache: Cache) -> None:
    scope: Scope = {
        "type": "http",
        "method": "HEAD",
        "path": "/path",
        "headers": [],
    }
    request = Request(scope)
    response = PlainTextResponse("Hello, world!")
    await store_in_cache(response, request=request, cache=cache)

    cached_response = await get_from_cache(request, cache=cache)
    assert cached_response is not None
    assert ComparableStarletteResponse(cached_response) == response

async def hi(request):
        capture_message("hi", level="error")
        return PlainTextResponse("ok")

async def plaintext(request, call_next):
        if request.url.path == "/":
            return PlainTextResponse("OK")
        response = await call_next(request)
        response.headers["Custom"] = "Example"
        return response

# headers in the response.
        if self.allow_all_headers and requested_headers is not None:
            headers["Access-Control-Allow-Headers"] = requested_headers
        elif requested_headers is not None:
            for header in [h.lower() for h in requested_headers.split(",")]:
                if header.strip() not in self.allow_headers:
                    failures.append("headers")

        # We don't strictly need to use 400 responses here, since its up to
        # the browser to enforce the CORS policy, but its more informative
        # if we do.
        if failures:
            failure_text = "Disallowed CORS " + ", ".join(failures)
            return PlainTextResponse(failure_text, status_code=400, headers=headers)

        return PlainTextResponse("OK", status_code=200, headers=headers)

async def daily_python_list(req):
    """Python 日报列表, 其实就是个按照日期伪造的页面, 用来订阅 rss"""
    language = req.path_params['language'].lower()
    if language not in {'cn', 'en', 'any'}:
        return PlainTextResponse('language should be cn / en / any.')
    limit: int = int(req.query_params.get('limit') or 10)
    xml_data: dict = {
        'channel': {
            'title': 'Python Daily',
            'description': 'Python Daily Newspaper',
            'link': f'https://{ONLINE_HOST}/newspaper/daily.python.list.rss.{language}',
            'language': {
                'cn': 'zh-cn',
                'any': 'zh-cn'
            }.get(language, 'en'),
        },
        'items': []
    }
    for date_delta in range(1, limit):
        title_date: str = ttime(time.time() - 86400 * date_delta)[:10]
        # 当日 0 点发布前一天的结果

async def user(request):
    user_id = request.path_params["user_id"]
    return PlainTextResponse(user_id)

async def method_not_allowed(self, request: Request) -> Response:
        # If we're running inside a starlette application then raise an
        # exception, so that the configurable exception handler can deal with
        # returning the response. For plain ASGI apps, just return the response.
        if "app" in self.scope:
            raise HTTPException(status_code=405)
        return PlainTextResponse("Method Not Allowed", status_code=405)