All requests processed by Crax, even errors, end with a Response object. If you are writing handlers that inherit from Crax Views you must return a Response (if not the default). If you write your own views that do not inherit from Crax views, you must return a Response as well. Thus, you should always return it. There is only one way not to return a response object: this is to work with Start and Send objects according to the ASGI specification. If you’re wondering how to write views without a Response object, or if you want to create your own Response type, see the ASGI Response documentation.

All of the Crax response types are inheriting from BaseResponse.



Takes initial arguments. request:

An instance of Crax Request. All of responses takes as first argument request parameter. May be set to None.


Type of string, bytes or dict. This is what you want to send in the response body.


Type of string. Sets response content type.


Type of int. Set the status code you want to send. There is one rule of thumb when you cannot override the status code. The Crax Request has no attribute, but if it exists and its value is in the range [200:227], the response status code will be set with this value. Otherwise, the response status code will be set.

Has methods.

Where content is the type of string or bytes. Converts content string to bytes if it is not yet.

set_cookies(key: str, val: str = “”, rest: dict):

Sets the “set-cookie” value for headers from the given parameters. Where key is a string type. Where value is a string type. The rest is a dictionary. You can pass any available cookie values ​​with this argument as key-value pairs. If your value is incorrect or not supported, no error occurs. Any invalid cookie parameters will be skipped.



Overrides nothing from the BaseResponse. Content type value equals to “text/html”.



Overrides the render() method.


Accepts any JSON serializable mapping as an argument. Converts it to JSON. Encodes JSON to bytes. Then it returns the encoded string.

from crax.views import BaseView
from crax.response_types import TextResponse, JSONResponse

# Example of usage in Crax Based Views
class MyCraxView(BaseView):
    methods = ['GET', 'POST']

    async def get(self):
        response = TextResponse(self.request, "Hello world")
        return response

    async def post(self):
        response = JSONResponse(self.request, {"Hello": "World"})
        return response

# Example of usage in Custom Views
class MyCustomClassView:
    methods = ['GET', 'POST']

    def __init__(self, request):
        self.request = request

    async def __call__(self, scope, receive, send):
        if self.request.method == "GET":
            response = TextResponse(self.request, "Hello world")
            await response(scope, receive, send)
        elif self.request.method == "POST":
            response = JSONResponse(self.request, {"Hello": "World"})
        return response

async def my_custom_coroutine_view(request, scope, receive, send):
    if request.method == "GET":
            response = TextResponse(self.request, "Hello world")
            await response(scope, receive, send)
    elif request.method == "POST":
        response = JSONResponse(self.request, {"Hello": "World"})
        return response



Overrides the initial arguments. Instead of Request object, the path is used as the first argument.


Type of string. The path to the file you want to process. If the file is not found, a FileNotFoundError exception will be raised. If file is found. If the file has not been modified, since the date of the request headers “If-Modified-Since” value response status code will be set to 304. Otherwise, the status code will be set to 200.

headers = {
    "If-Modified-Since": "Fri, 10 Jul 2122 12:05:43 GMT",
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0",
resp = requests.get(host, headers=headers)
assert resp.status_code == 304

headers = {
    "If-Modified-Since": "Fri, 10 Jul 2012 12:05:43 GMT",
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0",
resp = requests.get(host, headers=headers)
assert resp.status_code == 200

So, if file exists it will be sent by chunks with chunk size that equals 4096.

from crax.response_types import FileResponse
from crax.utils import get_settings_variable

async def get_latest_patch(request, scope, receive, send):
    base_url = get_settings_variable('BASE_URL')
    response = FileResponse(f'{base_url}/patches/latest.tar.gz')
    await response(scope, receive, send)



Only response type that does not inherit from BaseResponse. However, the first argument must be an instance of Request. The main difference from the rest response types is that StreamingResponse takes a content argument with asynchronous generator type.


Takes as argument type of async generator. Thus any object that provides __aiter__ and __anext__ methods could be passed as content argument.


Type of content you are going to steam. Default is None.

Let’s create simple example that streams up to 10 numbers to your browser

<!-- Your index.html -->
<ul id="streamResults"></ul>
    var streamResults = document.getElementById("streamResults")
    document.addEventListener("DOMContentLoaded", function () {
        streamResults.innerHTML = ""
        var e = new XMLHttpRequest
        e.overrideMimeType("text/plain"),"GET", "/get_stream"),
        e.seenBytes = 0, e.onreadystatechange = () => {
            if (3 === e.readyState) {
                var t = e.response.substr(e.seenBytes)
                    streamResults.innerHTML += "<li>" + t + "</li>"
                e.seenBytes = e.responseText.length
        }, e.addEventListener("error", e => {
        }), e.send()
# Your

class StreamView:
    def __init__(self, request):
        self.request = request

    async def create_stream():
        for n in range(10):
            yield str(n)
            await asyncio.sleep(1)

    async def __call__(self, scope, receive, send):
        stream = self.create_stream()
        response = StreamingResponse(self.request, stream)
        await response(scope, receive, send)

class ShowStream(TemplateView):
    template = 'index.html'
# Your

Route(Url('/'), ShowStream),
Route(Url('/get_stream'), StreamView),

You can find a more complex example of Streaming Response in the Crax github repository. This example shows how you can run tests and transmit test results in real time to any number of connected browsers.