Python Flask Intentional Empty Response

Question

Is there a way to return a response (from make_response() object or similar) with certain properties so that it doesn't render the page again and doesn't do anything else either. I am trying to run a code on the server without generating any output

A simple 'return None' produces:

ValueError: View function did not return a response

This should be possible because the following only downloads a file and doesn't render the template:

myString = "First line of a document"
response = make_response(myString)
response.headers["Content-Disposition"] = "attachment; filename=myFile.txt"
return response

Solution

You are responding to a request, your HTTP server must return something. The HTTP 'empty response' response is 204 No Content:

return ('', 204)

Note that returning a file to the browser is not an empty response, just different from a HTML response.

Comments

[dtk]

Ftr: you may use httplib.NO_CONTENT to avoid the magic number.

[bfontaine]

Note the equivalent of Python 2’s httplib.NO_CONTENT in Python 3 is http.HTTPStatus.NO_CONTENT.

[Martijn Pieters]

@bfontaine: or http.client.NO_CONTENT

[Martijn Pieters]

@bfontaine: at the bottom of the http package docs; these used to be the normal location until the HTTPStatus enum was introduced, see github.com/python/cpython/commit/…