[Twisted-web] Deferred 101

mayvimmer at fibertel.com.ar mayvimmer at fibertel.com.ar
Tue Jul 5 00:14:18 EDT 2011

Hi guys,
 I'm totally new to Twisted although everything I try so far has been a lot of
fun. I have a really simple situation it seems I cannot wrap my head around.
Although the tutorial have been really helpful I cannof find how to fix this
last part.

I created a "login" method that connects with my db through adbapi and
returns a deferred. I'm using it with pyamf and it's working ok. Now I have to
implement the same thing but accept logins through a standard web page. I
followed the Twisted web in 60 seconds tutorial and created a render_POST
method that processes the login method. The only catch is that I'm returning a
mako template page. Ok, finally my problem: I cannot make it return the result
of the deferred: if I debug the response I see a "<Deferred at ...>" but
not the intended message. Actually if I add a callback method that just prints
the response, I can get it (but since that prints the message in the log, it
doesn't help). What am I missing?

Here's some code to help me explain my problem:

class Login(Resource):
    """LogIn post processing"""
    isLeaf = True

    def render_POST(self, request):
        rsp = None
        errc = None
        usr = User()
        username = cgi.escape(request.args['username'][0])
        passwd = cgi.escape(request.args['passwd'][0])
            # here I get the answer of the process. I would expect the login
            # message but instead I get a deferred repr object.
            rsp = usr.login(request, username, passwd)
        except Exception, e:
            errc = e.args[0]
        # this should return the contents of postproc.mak (a regular file) 
        # but with certain keywords replaced.
                **{'status':rsp, 'username':username,
        return NOT_DONE_YET

class Userobject):

    def login(self, request, username, password):
        rp = defer.Deferred()

        def cb(rs):
            resp = u'Unidentified reason'
            if len(rs)==0:
                resp = u'No account exists for the given username'
            elif rs[0]['password'!=password:
                resp = u'Password does not match'
                resp = u'Ok'

        def eb(failure): rp.errback(failure)

        d = self.conn_pool.runQuery('select password from user where '
                        'username=?', (username,))

        return rp

Eduardo Miguez

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