Python WSGI Error on Output

Question

My python has become quite rusty as I haven't used it for quite a while and am stuck with an issue I am not able to figure out.

The python program should accept a form's data sent by a web page, and return some JSON response codes back to it. Everything works fine except when the data is sent:

def application(environ, start_response):
    """ Process the form data, spit out the reponse """

    # code here extracts the form 
    # data and the response code is 
    # stored in info

    # everything done, output now
    output(environ, start_response, info)


def output(environ, start_response, info):
    
    # debug
    print >> environ['wsgi.errors'], "BACK TO THE BROWSER"

    feedback = json.dumps(info)
    
    # debug
    print >> environ['wsgi.errors'], feedback
    
    status = "200 OK"
    headers = [('Content-Type', 'application/json; charset=UTF-8'), ('Content-Length', str(len(feedback)))]
    start_response(status, headers)
    return [feedback]

The error log says:

...
[wsgi:error] ... BACK TO THE BROWSER

[wsgi:error] ... {"errors": [1430360477881, 1430233459050]}

[wsgi:error] ... mod_wsgi (pid=1654): Exception occurred processing WSGI script '/tmp/mod_wsgi-localhost:8000:0/htdocs/'.

[wsgi:error] ... TypeError: 'NoneType' object is not iterable
...

Ok, Python is complaining that something it expects to be iterable is None. But which iterable is Python complaining about in this function? (Note that I am using mod_wsgi directly without any frameworks / modules).

ljk321 · Accepted Answer · 2015-04-30 06:31:01Z

3

You need to return the response:

return output(environ, start_response, info)

answered Apr 30, 2015 at 6:31

ljk321

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3 Comments

Sam Over a year ago

So basically, for WSGI the input and the output both have to be from the same function (application() here, in the case of mod_wsgi)?

ljk321 Over a year ago

WSGI requires application to take the request and return an iterable response.

ljk321 Over a year ago

More details can be found in PEP 3333

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