How to override notfound() in web.py for a REST API? - json

Question

I trying to understand how to deal with HTTP error codes using web.py as a REST framework. I can easily use try/catch blocks to return HTTP 404, 400, 500, etc... but I am having a hard time sending a custom JSON message with it.
import web
import json
urls = (
'/test/(.*)', 'Test'
)
app = web.application(urls, globals())
def notfound():
return web.notfound(json.dumps({'test': 'test'}))
class Test:
def GET(self, id):
web.header('Content-Type', 'application/json')
return self.get_resource(str(id))
def get_resource(self, id):
result = {}
if id == '1':
result = {'1': 'one'}
elif id == '3':
return web.notfound()
return json.dumps(result)
if __name__ == '__main__':
web.config.debug = False
app.notfound = notfound
app.run()
This works fine, but when id == 3, I cannot override the behaviour, and the Content-Type header is duplicated:
# curl -i -H "Accept: application/json" http://localhost:8080/test/3
HTTP/1.1 404 Not Found
Content-Type: application/json
Content-Type: text/html
Transfer-Encoding: chunked
Date: Mon, 09 Sep 2013 23:59:28 GMT
Server: localhost
404 Not Found
How can I return a JSON Content-Type, with a custom message?

Answer 1

HTTP Errors in web.py should be raised as exceptions.
I used this class to decorate json error (it has specific output format in my app, so you may adopt it to your needs):
class NotFoundError(web.HTTPError):
'''`404 Not Found` error.'''
headers = {'Content-Type': 'application/json'}
def __init__(self, note='Not Found', headers=None):
status = '404 Not Found'
message = json.dumps([{'note': note}])
web.HTTPError.__init__(self, status, headers or self.headers,
unicode(message))
I have created a simple json api with web.py you may want to check, believe me it has some interesting ideas.