Python Cherrypy: 500 ValueError: Page handlers MUST return bytes

Question

I'm getting the following error from my cherrypy script that is being generated by the submit module.

ValueError: Page handlers MUST return bytes. Use tools.encode if you wish to return unicode

I turned tool.encode on in my config but I'm still getting this error. I'm allowing users to upload content via the jQuery Form Plugin. Anythoughts as to why I'm getting this error?

Here is my cherrypy file:

class Root(object):    

@cherrypy.expose
def index(self)
    return open('/home/joestox/webapps/freelinreg_static/index.html')

@cherrypy.expose
def submit(self, myfile):

    cherrypy.session['myfile'] = myfile
    data_name = myfile.filename

    #Send back to JQuery with Ajax
    #Put in JSON form
    data_name= json.dumps(dict(title = data_name))
    cherrypy.response.headers['Content-Type'] = 'application/json'

    return data_name



cherrypy.config.update({
    'tools.staticdir.debug': True,
    'log.screen': True,
    'server.socket_host': '127.0.0.1',
    'server.socket_port': *****,
    'tools.sessions.on': True,
    'tools.encode.on': True,
    'tools.encode.encoding': 'utf-8',
})

config = {
}

cherrypy.tree.mount(Root(), '/', config=config)
cherrypy.engine.start()

HTML:

<!DOCTYPE html>
    <html>
        <head> 
            <script type='text/javascript' src='freelinreg_static/google.js'></script>
            <script type='text/javascript' src='freelinreg_static/frontend.js'></script>
            <script type='text/javascript' src='freelinreg_static/malsup.js'></script>
        </head>
        <body>

        <form id="dataform" action="submit" method="post" enctype="multipart/form-data">
            <input type="file" name="myfile" id="myFile"/>
            <input type="submit" id="data_submit" value="Continue"/>
        </form>                          

        </body>
    </html>

jQuery (frontend.js):

$(document).ready(function () {
    (function () {
        $('#dataform').ajaxForm({
            url: "submit",
            success: function (data) {
                var $a_var = data['title'];
                $('body').append($a_var);
            }
        });
        return false;
    })();
});

score 8 · Answer 1 · edited Jan 01 '21 at 03:17

8

I my case the issue started after switching from python2 to python3.

It was resolved by setting

    'tools.encode.text_only': False

In the app global configuration.

Hope it helps

edited Jan 01 '21 at 03:17

colio303

81
10

answered Mar 07 '19 at 08:47

drorsun

881
1
8
22

1

After looking at the other answers this is what worked for me. Thank you. – julian May 18 '21 at 22:35

score 5 · Answer 2 · answered Jul 13 '18 at 08:31

5

Hi people looking for answers. I had the same problem but in my case this little addition solved everything.

return <some-json>.encode('utf8')

answered Jul 13 '18 at 08:31

JtotheR

503
5
5

Use json_out tool instead and just return a dict – webknjaz -- Слава Україні Aug 07 '18 at 10:22
1

@webKnjaZ well fixed my problem, I had the same error and these two words fixed it so I was happy – JtotheR Aug 14 '18 at 15:24
Yes, it's just not the best way to go architecturally. – webknjaz -- Слава Україні Aug 15 '18 at 13:20

score 4 · Accepted Answer · edited Aug 14 '18 at 10:07

4

You need to rearrange global config update to happen after application mount:

config = {
}

cherrypy.tree.mount(Root(), '/', config=config)

cherrypy.config.update({
    'tools.staticdir.debug': True,
    'log.screen': True,
    'server.socket_host': '127.0.0.1',
    'server.socket_port': *****,
    'tools.sessions.on': True,
    'tools.encode.on': True,
    'tools.encode.encoding': 'utf-8'
})

cherrypy.engine.start()

Because you were calling config = {} after your config update command you were overriding the update settings for Root application.

Also, change your submit function to this:

@cherrypy.expose
@cherrypy.tools.json_out
def submit(self, myfile):
    cherrypy.session['myfile'] = myfile

    # Return dict, which will be autoconverted to JSON
    # by the json_out tool (see decorator above)
    return {'title': myfile.filename}

edited Aug 14 '18 at 10:07

webknjaz -- Слава Україні

687
4
34

answered Nov 26 '13 at 13:41

Andrew Kloos

4,189
4
28
36

Thanks for the tip! Makes a lot of sense! Unfortunately I'm still getting the same 500 ValueError. – natsuki_2002 Nov 26 '13 at 14:08
It worked! Anyways to send the data back to jQuery as a JSON dict still? Now the jQuery doesn't seem to realize that its a JSON dict. – natsuki_2002 Nov 26 '13 at 16:29
1

Yes, you should use... JSONobj = JSON.parse(data); alert(JSONobj.title); – Andrew Kloos Nov 26 '13 at 17:12
To return json from dict use json_out tool – webknjaz -- Слава Україні Aug 07 '18 at 10:21

Python Cherrypy: 500 ValueError: Page handlers MUST return bytes

3 Answers3