how to handle javascript callback return data in python - google-app-engine

Question

var req = new XMLHttpRequest();
req.open('GET', '/Search?' + query, async);
if (async) {
req.onreadystatechange = function() {
if(req.readyState == 4 && req.status == 200) {
var response = null;
try {
response = JSON.parse(req.responseText);
} catch (e) {
response = req.responseText;
}
callback(response);
This callback function returns values to my python code (I am using GAE with python 2.7).
class KeywordSearchRPCHandler(webapp2.RequestHandler):
def __init__(self):
webapp2.RequestHandler.__init__(self)
self.methods = RPCMethods()
def get(self):
func = None
action = self.request.get('action')
if action:
if action[0] == '_':
self.error(403) # access denied
return
else:
func = getattr(self.methods, action, None)
if not func:
self.error(404) # file not found
return
else :
args = ()
while True:
key = 'arg%d' % len(args)
val = self.request.get(key)
#print val
if val:
args = (json.loads(val))
else:
break
result = func(*args)
self.response.out.write(json.dumps(result))
This is the code that handles the callback function.
I get the error init() takes exactly 1 argument (3 given)
Could you please help me modify my code. Thanks a lot in advance.

Answer 1

Here is the documentation: Docs
webapp2.RequestHandler.__init__(request=None, response=None) is the signature.
So add request and response as parameters to your init and you should be fine.
Change def __init__ (self) to def __init__(self, request=None, response=None). This will fix the bug.
And you probably want to call super properly instead of calling __init__ on the class here: webapp2.RequestHandler.__init__(self)
This should most likely be super(KeywordSearchRPCHandler, self).__init__(request, response) instead.

Answer 2

The init handler:
class RPCHandler(webapp2.RequestHandler):
""" Allows the functions defined in the RPCMethods class to be RPCed."""
def __init__(self, request, response):
super(RPCHandler, self).__init__(request, response)
self.methods = RPCMethods()
But I do not understand your json.loads(val) in your GET, because you send a query string and not a json request.
Below is an example post, handling a json post:
def post(self):
data = self.request.body
args = loads(data)
if 'action' not in args:
self.error(405) # access denied
return
func = args['action']
if func[0] == '_':
self.error(403) # access denied
return
func = getattr(self.methods, func, None)
if not func:
self.error(404) # file not found
return
# action handler aanroepen
result = func(args)
self.response.out.write(json.dumps(result))
If you use a GET with a query string webapp2 will handle the request. From the docs:
# An iterable with all items in the MultiDict:
# [('check', 'a'), ('check', 'b'), ('name', 'Bob')]
self.request.GET.items()