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Re: [nycpython] rocket

From: Patrick
Sent on: Saturday, August 28, 2010 10:53 AM

I'm listening to Revolver on ExtensionFM while I am navigating your
most awesome walkthru of Rocket.

I'm hoping to use your library with facebook, will it work with o-auth?

On Wed, Aug 25, 2010 at 3:18 AM, James Dennis <[address removed]> wrote:
> Hey Everyone -
> James Dennis here. I felt as though I let the community down with my shoddy
> presentation tonight so I have decided to write?about Rocket and share my
> thinking in a more cohesive form. It's going to be a somewhat long email so
> no worries if it's too long for anyone. I feel the need to properly explain
> the system to the community, especially after finding something quite
> similar implemented in xmlrpclib. Thanks to David Christian for showing me
> that.
> http://hg.python....­
> First, an overview
> When I got into Python, I was attempting to earn money programming and
> wanted to do so using Python. I enjoy building things, so I was eager to
> build ways of communicating with Twitter and Facebook, etc. I found myself
> implementing remote API's frequently and doing the whole thing. Perhaps I
> could've downloaded a library, but I was teaching myself Git and didn't
> really know how to work my way around the world of Python yet. Excuse,
> excuse... Anyway, I ended up writing this a lot.
>>>> import urllib
>>>> import simplejson
>>>> query_url = 'http://search.twi...­'
>>>> results_json = urllib.urlopen(query­_url).read()
>>>> results = simplejson.loads(res­ults_json)
>>>> results['results'][0­]
> {'iso_language_code'­: 'en', 'text': "Every time I talk about Rocket, I find
> out this work was done for XML. In fact, Python's xmlrpc seems to have
> extremely similar code.", 'created_at': 'Wed, 25 Aug[masked]:43:03 +0000',
> 'profile_image_url':­
> 'http://a0.twimg.c...­',
> 'source': '&lt;a href=&quot;;­
> rel=&quot;nofoll­ow&quot;&gt;­Tweetie for Mac&lt;/a&gt;­', 'from_user':
> 'j2labs', 'from_user_id':[mask­ed], 'to_user_id': None, 'geo': None, 'id':
>[masked], 'metadata': {'result_type': 'recent'}}
> This got old quickly.
> I found myself implementing many client-side api's for systems that didn't
> have a full python solution. Event Brite, Machine Translation services like
> Moses or Apertium (I dabbled with Machine Translation in the past) and I
> started to get curious as to how I could save time. I didn't really want to
> muck about with how I handle communicating with services more than once. So
> when I needed event brite for a project, using Python, I implemented
> pyventbrite. Pyventbrite gets it's inspiration from pyfacbeook, written
> by?Samuel Cormier-Iijima and many others. In here is where I first came
> across IDL's in Python. Some people say they are Interface Description
> Languages. I have heard college professors say Interface Domain Language.
> Wikipedia suggests that Interface Definition Language is also used. Anyway,
> pyfacebook is where I first saw Rocket's proxy function technique.
> The time came for me to implement the Event Brite API so I stripped down
> pyfacebook to just the core of what I'd need for a json system and
> pyventbrite is where I ended up. The Facebook API had a lot?of stuff in it
> that was unnecessary for me, so I removed as much as I could. I really just
> wanted a way to generate the functionality for reaching out to a remote host
> as quickly as possible while providing some security over whether or not my
> inputs made sense.?I then had to implement the Sailthru API for Python but
> there didn't seem to be a Python driver around. Here we go again...
> After making some modifications to pyventbrite, splitting the core of it's
> functionality into a separate module and finally arriving at an
> implementation of Sailthru, I had the first draft of Rocket.
> A quick refresher on __call__
> To recall, we know that Python's __call__() is a function that gets called
> when you call an object. __call__() can make an object callable.?Let's take
> a quick look.
>>>> class SomeClass(object):
> ... ? ? def foo(self):
> ... ? ? ? ? ? ? print 'foo'
> ... ? ? def __call__(self):
> ... ? ? ? ? ? ? print 'You called __call__()'
> ...
>>>> sc = SomeClass()
> foo
>>>> sc()
> You called __call__()
> You can call an instance of SomeClass and it will be treated like a
> function. This concept is core to the foundation of Rocket because the Proxy
> class instances are an instance of proxy being called like a function. We'll
> get to what that means in a second.
> Looking from the top down
> Rocket ::­
> PySailThru ::?­
> A user of pysailthru, which is a module for Sailthru that implements Rocket,
> would write code like this:
>>>> api_key = ''
>>>> api_secret_key = ''
>>>> email = '[address removed]'
>>>> sailthru = Sailthru(api_key, api_secret_key)
>>>> email =­mail)
> An implementer of pysailthru has some work to do, but not too much. Lines
>[masked] in pysailthru (link below) and you see the IDL for pysailthru. The
> IDL is most of the work. That's how I feel it should?be for someone to
> implement an API.
> Proxy's
> The IDL for pysailthru starts with the following:
> ?? ?'email': {
> ?? ? ? ?'get': [
> ?? ? ? ? ? ?('email', str, []),
> ?? ? ? ?]
> ...
> That's the same function I called above. So how does this dictionary of
> dictionarys of lists get turned into something callable? We generate some
> code! This is why pysailthru calls rocket.generate_prox­ies() immediately
> after defining the IDL on lines 111-113.
> rocket.generate_prox­ies(FUNCTIONS,
> ?? ? ? ? ? ? ? ? ? ? ? ?_get_api_docstring,­
> ?? ? ? ? ? ? ? ? ? ? ? ?foreign_globals=glo­bals())
> _get_api_docstring is a function that attempts to build a URL that maps to
> the remote function's documentation. In the case of sailthru, the
> documentation exists for email.get exists at
> http://docs.sailt...­, so we can easily supply the url
> of the documentation by inserting the namespace and the method into the URL.
> The implementation of _get_api_docstring on line 27 will show that.
> Anyway, back to the Proxy's. The Proxy objects in Rocket are defined
> (potentially confusing elements removed) like this:
> class Proxy(object):
> ?? ?"""Represents a namespace of API calls."""
> ?? ?def __init__(self, client, name, gen_namespace_pair=g­en_namespace_pair):
> ?? ? ? ?self._client = client
> ?? ? ? ?self._name = name
> ?? ?def __call__(self, method=None, args=None, add_session_args=Tru­e):
> ?? ? ? ?return self._client('%s.%s'­ % (self._name, method), args)
> Let's take a look at that last line in __call__. If a method is passed in,
> we call _client with two arguments; a string and args. _client is actually
> our Sailthru object, so we are calling Sailthru.__call__() when we call
> _client like a function! Remember this?
> sailthru = Sailthru(api_key, api_secret_key)). This call is actually
> like:?Sailthru.__cal­l__('­get', args).
> Sailthru.__call__() is actually Rocket's __call__, which is defined on lines
> 289-330. This function takes ''­, splits it into
> 'sailthru', 'email' and 'get' and then starts constructing the actual web
> request. It then sends the web request, parses the output and gives it back
> to the user as a native Python structure.
> But wait a sec... How did the arguments get here? What called Proxy.__call__
> or Proxy()? That's coming in a moment...
> A series of __call__()'s
> In Rocket's __init__ function, you will see the following lines
> for namespace in self.function_list:
> ?? ?(ns_name, ns_title) = self.gen_namespace_p­air(namespace)
> ?? ?self.__dict__[ns_na­me] = eval('%sProxy(self, \'%s\')'
> ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?% (ns_title,
> ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? '%s.%s' % (client, ns_name)))
> After the modules are in Rocket's namespace, it instantiate's them and
> attaches them to the Rocket instance. In this case, the Rocket instance is
> our Sailthru object, which subclasses Rocket.
>>>> sailthru = Sailthru('', '')
> KeyboardInterrupt
>>>> sailthru
> <pysailthru.Sailt­hru object at 0x1011d47d0>
> <rocket.rocket.Em­ailProxy object at 0x1011d4d50>
> <bound method EmailProxy.get of <rocket.rocket.Em­ailProxy object at
> 0x1011d4d50>>
> So, we see the generated Proxy objects are attached to the client in Rocket,
> but how did get EmailProxy? That happened in generate_proxies, which was
> called when the module was loaded but before Sailthru was insantitated.
> generate_proxies()
> When pysailthru is first loaded, we get EmailProxy as a result of pysailthru
> calling generate_proxies() in it's loading process. The call loops over the
> namespaces (email, send, blast, ...), which requires another loop over the
> functions (http methods) and then a final loop over each argument for each
> function. Code is generated that looks like this, for email.get:
> def get(self, email):
> ?? ?"""Sailthru call. See http://docs.sailt...­"""
> ?? ?args = {}
> ?? ?args['email'] = email
> ?? ?return self('get', args)
> email.get() has no optional values and simply takes a string for it's
> argument. A more complicated function might look like this:
> def post(self, email, vars=None, lists=None, templates=None):
> ?? ?"""Sailthru call. See http://docs.sailt...­"""
> ?? ?args = {}
> ?? ?args['email'] = email
> ?? ?if isinstance(vars, list) or isinstance(vars, dict): vars =
> json_encode(vars)
> ?? ?if vars is not None: args['vars'] = vars
> ?? ?if isinstance(lists, list) or isinstance(lists, dict): lists =
> json_encode(lists)
> ?? ?if lists is not None: args['lists'] = lists
> ?? ?if isinstance(templates­, list) or isinstance(templates­, dict): templates
> = json_encode(template­s)
> ?? ?if templates is not None: args['templates'] = templates
> ?? ?return self('post', args)
> In this function ( we see special handling for vars, lists and
> templates. First, they are listed as keyword arguments to post(). This is
> because they are all also defined as 'optional' in the IDL. We also see that
> they might come in the form of a list or a dict. In the cases where
> instances is not provided, we simply don't add them to post()'s output. The
> output of post() is the data we intend to send along to
> The body of the function, according to the inner-most loop, is a list of
> lines of code called 'body'. The first line is args = {}. We see this on
> line 159, before the loop around a functions arguments begins. It then loops
> over the arguments to fill in their behavior.
> The first check looks at the arguments options, like whether or not the
> argument is optional or has a default value. This list can be empty, but for
> optional arguments it will contain the string 'optional' like ['optional'].
> It might be a tuple where the first element is 'default' with the second
> element containing argument's default value. This might look like
> [('default', 1)] or something like that.?The second check is for the param
> type. If the param type is rocket.json, we know to json encode the structure
> given.?The third argument check is simply for whether or the not the value
> is optional.
> After the body is written, we have a list that represents the function body,
> but it doesn't have a definition line yet. First, we insert the generated
> doc string at the beginning of this list (see _get_api_docstring for
> details). Then we insert the function's definition line (def get(...)). The
> function's definition is essentially a collection of argument names that are
> required and then some keyword arguments representing the optional arguments
> in the IDL. vars, lists and templates were all optional for, so
> we see them passed as vars=None, etc.
> Once the loop over a namespace's functions is complete, Rocket then calls
> exec on the function body to instantiate it. I think this particular portion
> of the code could be made neater, but it currently calls eval() with the
> assumed method name (get for email.get) and puts the output into a list
> function instances it uses at the next layer of the loop. When it finally
> reaches completes a loop iteration for the namespace (the outermost loop at
> this point), the generated code is instantiated as a new type called
> NamespaceProxy (really, this is EmailProxy).
> Namespaces
> We see the following lines at the end of generate_proxies().
> proxy = type('%sProxy' % ns_title, (Proxy, ), methods)
> globals()[proxy.__na­me__] = proxy
> foreign_globals[prox­y.__name__] = proxy
> Less common use of type() here. type(), when called with one argument, will
> tell you the type of some structure. type(), called with three arguments,
> type functions as a constructor.
> http://docs.pytho...­
> Now, let's recall that Proxy is a class created to give us __call__, and
> this Proxy's __call__ then calls Rocket.__call__ which then makes the actual
> web connection for us. We saw this definition above, but I will copy the
> important parts here too:
> class Proxy(object):
> ?? ?def __call__(self, method=None, args=None, add_session_args=Tru­e):
> ?? ? ? ?return self._client('%s.%s'­ % (self._name, method), args)
> The call to type() then instantiates '%sProxy' % ns_title, where ns_title is
> the namespace with .title() applied, giving us EmailProxy. EmailProxy is a
> subclass of the following classes (Proxy, ) and has methods for members.
> This gives us an EmailProxy with get and post defined, but it's not
> available to code until we put it in the namespace.
> It might be controversial to require globals() from a module implementing
> Rocket, but that is how it is designed as of now. After the Proxy object is
> put into the namespace of pysailthru (foreign_globals[pro­xy.__name__] =
> proxy), the __init__ function for Sailthru can then instantiate all of the
> proxy objects in it's __init__, even though they were constructed inside
> Rocket's namespace.
> Remember the code in Rocket's __init__ that looked like below?
> for namespace in self.function_list:
> ?? ?(ns_name, ns_title) = self.gen_namespace_p­air(namespace)
> ?? ?self.__dict__[ns_na­me] = eval('%sProxy(self, \'%s\')'
> ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?% (ns_title,
> ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? '%s.%s' % (client, ns_name)))
> Once this part is complete, the Sailthru object now has a member called
> EmailProxy, which has the functions 'get()' and 'post()'.
> Before we're done, let's jump back to the definition for:
> def get(self, email):
> ?? ?"""Sailthru call. See http://docs.sailt...­"""
> ?? ?args = {}
> ?? ?args['email'] = email
> ?? ?return self('get', args)
> That last line is a __call__(). So the chain of __call__()'s is finally
> complete.
> Quick recap
> 1) The IDL is defined.
> 2) The module implementing an API with Rocket generates the proxy objects
> from the IDL
> 3) These objects, called NamespaceObject, each have get(), post(), delete(),
> put(), etc defined.
> 4) The Proxy objects exist in the global namespace.
> 5) When a subclass of Rocket is instantiated, the Proxy objects are attached
> to the subclass
> 6) subclass.namespace.m­ethod() is now callable.
> 7) subclass.namespace.m­ethod() is a function that validates inputs and then
> calls subclass.namespace('­method', args)
> 8) subclass.namespace('­method', args) then calls
> subclass('subclass.n­amespace.method', args)
> 9) subclass('subclass.n­amespace.method', args) calls out to the Internet to
> complete the request.
> 10) Rocket parses the returned result and returns a native python structure
> representing the response
> An implementation of a Rocket module
> So, we're almost done. The general logic is covered for the code generation
> techniques but an implementer shouldn't?have to care about that stuff.
> Implementers care about 1) obtaining the IDL whether by coding it or
> receiving it from a remote source and 2) implementing any protocol specific
> stuff like request signatures or how API URL's are constructed.
> In the case of Sailthru, the URL for email.get is
> http://api.sailth...­. We know the namespace is email, so we just
> put the namespace there in the gen_query_url callback. See line 169 in
> pysailthru.
> Each request must be signed for Sailthru to accept them, so build_query_args
> is essentially a way of passing a sign_sorted_args as the signing algorithm.
> See from Rocket for argument signing functions. There's some more
> stuff in there, but it's not full featured yet.
> check_error implements Sailthru's error response, which is to send json with
> the key 'error' in it.
> So, to recap quickly for implementers, you probably only need to define the
> IDL, gen_query_url, build_query_args and a function that can handle errors
> from the server called check_error.
> Fin.
> I am very interested in hearing about improvements, thoughts, criticisms,
> etc. Passing globals() seems nasty, but I don't have a clean solution here
> yet.
> Anyway,
> James (@j2labs)
> --
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> Python Meetup Group.
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