Convert to Twisted Asynchronous Design

Question

Good. I have a problem expressing my problems with the code I'm working on without dumping a ton of code; therefore, this is what will happen synchronously (instead of asking for it in terms of its asynchrony).

Also for classes, when should a variable be accessible through a method argument and when should it be accessible through an instance variable?

Synchronously, it will look like this ... Note: the actual server URLs and parsing are different, but just complicate things. Also in the following example, the get_token method accepts the session as a parameter, should it use the session instead using self.session?

import urllib
import time

class SyncExampleClass(object):

    def __init__(self):
        self.session = None
        self.token = None
        self.session_time = -1


    def get_session(self):
        s = urllib.urlopen("http://example.com/session/").read()
        self.session_time = int(time.time())
        return s

    def get_token(self, session):
        t = urllib.urlopen("http://example.com/token/?session=%s" % session).read()
        return t

    def construct_api_call(self, api_method):
        # if the session is over an hour old (is that the correct sign?)
        if time.time() - 3600 > self.session_time or self.session is None:
            self.session = get_session()
            self.token = get_token(self.session)

        call = urllib.urlopen("http://example.com/api/?method=%s%session=%s&token=%s" % (api_method, self.session, self.token) ).read()
        return call

Answer 1

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from twisted.internet import defer
from twisted.web import client
from twisted.python import log
from urllib import urlencode
import time

class APIException(Exception):
    pass

class ASyncExampleClass(object):
    def __init__(self):
        self.session = None
        self.token = None

    @defer.inlineCallbacks
    def api_call(self, api_method,tries=3,timeout=10):
        attempt = 1
        while attempt <= tries:
            attempt += 1
            if self.session = None:
                yield sess_data = client.getPage("http://example.com/session/",timeout=timeout)
                self.session = extractSessionFromData(sess_data)
            if self.token = None:
                yield token_data = client.getPage("http://example.com/token/?%s" % urlencode(dict(session=self.session)),timeout=timeout)
                self.token = extractTokenFromData(token_data)
            # Place "the" call
            yield api_result = client.getPage("http://example.com/api/?%s" % urlencode(dict(api_method=api_method,session=self.session,token=self.token)),timeout=timeout)
            #
            if sessionInvalid(api_result):
                log.msg("Request for %s failed because invalid session %s" % (api_method,self.session))
                self.session = None
                self.token = None
                continue
            if tokenInvalid(api_result):
                log.msg("Request for %s failed because invalid token %s" % (api_method,self.token))
                self.token = None
                continue
            # Any other checks for valid result
            returnValue(api_result)
            break # Not sure if this is needed, not in an position to test readily.
        else:
            raise APIException("Tried and failed %s times to do %s" % (attempt - 1, api_method))

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twisted.web.client.getPage POST, , , HTTPClientFactory.

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