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Rocket is a Python framework for implementing client-side API's with a quickness
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Rocket is a library for quickly implementing a client-side API.

Rocket is licensed under the Apache Licence, Version 2.0

In short, Rocket is...

Rocket is a collection of modules that make interacting with remote API's easy. Rocket comes with a code generation system for using an IDL to describe the remote source's API.

There is complexity in implementing a remote API so Rocket tries to handle all of that for you and let you focus on what's unique about this particular API.

Let's say we want to connect to the Awesome API and fetch the top item off the 'cool stuff' list with HTTP GET. The IDL for this API might look like below:

    'get_awesome_list': {
        'get': [
            ('list_name', str, []),
            ('page', int, ['optional']),
            ('size', str, ['optional']),

This is what using the the Awesome API rocket would look like:

from r_awesome import AwesomeAPI
awesome_api = AwesomeAPI(api_key='some key', api_secret_key='SHHHHH')

response = awesome_api.get_awesome_list.get('cool stuff', page=1, size=1)

I have been able to implement entire API's with multiple namespaces in an afternoon using this method and found the total lines of codes to often be below half of the other implementation offerings.


Rocket comes with multiple API implementations, but they are not installed by default. Each module has a for installing but Rocket doesn't install them by default.

Currently packaged: Sailthru, Songkick, Echonest, Twilio, Twitter, Exfm.

If you're only looking to use one of these modules, then you can skip the rest of the documentation.

People looking to learn more about how Rocket works should continue reading and then checkout r_simple in the modules directory.

Rocket's design

Rocket uses an interface description language, specified by Rocket implementors, to generate Python code that implements each API call.

Rocket is designed to help programmers focus on the details of an API implementation, rather than the details of implementing an API.

If a remote API consists of only one namespace, called email, which goes over HTTP POST and takes two arguments email and vars, with vars being optional, your API implementation will look close to this.

That's as minimal as I've been able to get for describing an API. Perhaps a different structure could be used, but the idea remains the same. To describe the API in a language agnostic way and generate code that implements it.

An API implementer would then subclass Rocket, like class Sailthru(Rocket) and then override __init__() to pass that FUNCTIONS list to rocket for code generation.

An API user would not have to worry about this stuff, as it is behind the scenes of the Rocket framework.


To implement a Rocket you subclass Rocket and then make use of callbacks to adjust functionality. Most common are adjustments to how query urls are made, how errors are handled when you receive http 200 responses regardless of errors or how query arguments are handled before you send them to the remote source.

r_sailthru is a good example of how check_error, build_query_args and gen_query_url can be used. Here is how each one works.

def check_error(self, response):
    """Checks if the given API response is an error, and then raises
    the appropriate exception.
    if type(response) is dict and response.has_key('error'):
        raise rocket.RocketAPIException(response['error'], response['errormsg'])

We see that check_error receives a response, which was parsed from json into a python dict called response. We found that it had an error key, so we raise an exception containing the error info found in the dict.

def build_query_args(self, *args, **kwargs):
    """Overrides Rocket's build_query_arg to set signing_alg to
    return super(Sailthru, self).build_query_args(signing_alg=sign_sorted_values,
                                                  *args, **kwargs)

The sailthru API requires signing our requests, but Rocket makes no assumptions on signing by default. We override build_query_args to call build_query_args with sign_sorted_values for it's signing algorithm. sign_sorted_values, along with some other choices, are implemented in rocket.auth module.

def gen_query_url(self, url, function, format=None, method=None, get_args=None):
    """Sailthru urls look like 'url/function'.

    return '%s/%s' % (url, function)

The callback handles the data known about the call and generates the URL string that handles the call. Each API is different here, so this callback allows the flexibility of looking at the relevant information and generating what you think it is.

Namespace handling

Sometimes namespaces are complicated and instead of being simple like 'email' they have some complexity like group/subgroup.method. Or perhaps variables even turn up in the url like something/{user_id}/feed.json Rocket handles this by offering several functions to handle how that string is formatted into something that is compatible with the code generation.

It's easy enough to think of this functions as a namespace pair generator. We'll see this again in the next section.

Let's look at one: rocket.proxies.gen_ns_pair_multi_delim.

def gen_ns_pair_multi_delim(ns, delims=['\/', '\.']):
    def title_if_lower(nnss):
        if not nnss.isupper():
            return nnss.title()
        return nnss

    groups = re.split('|'.join(delims), ns)
    ns_fun = ''.join(groups)
    ns_title = ''.join([title_if_lower(g) for g in groups])
    return (ns_fun, ns_title)

The purpose of this function is to generate namespace keys from the string found in the FUNCTIONS list. If we see SMS/Messages, like found in r_twilio, we translate this to SMSMessages and SMSMessages which are then used for and SMSMessagesProxy, as attached to the Rocket.

We make use of this function by passing it in as part of Rocket's __init__().

class Twilio(rocket.Rocket):
    def __init__(self, *args, **kwargs):
        super(Twilio, self).__init__(FUNCTIONS,

Often enough, you won't need these overrides, but you'll be happy rocket handles a few of them easily when they come up.

Rocket doesn't implement the most flexible by default because it aims to keep performance light unless additional handling is desired.

URL's with Variables

Variables sometimes turn up in the way URL's are constructed. Like perhaps a feed system with<artist_id>/calendar.json. Rocket handles url's with variables with two helper functions.

Imagine we have this FUNCTIONS list.

    'artists/{artist_id}/calendar': {
        'get': [
            ('artist_id', str, []),

Rocket generates access to this namespace by replacing the {variable} with an underscore. We see this as Artists_CalendarProxy and artists_calendar.get().

This is done by using proxies.gen_ns_pair_multi_vars as the namespace pair generator. This function can handle multiple delimiters, like '/', and handles variables where a regex can describe them. In this case, I'm using Rocket's default which is '{(\w+)}'.

Rocket then implements gen_query_url to fill in the variable's values with values from the caller. This means {artist_id} gets replaced with the artist's id.

artist_id = '258948'

This gets translated to a URL like:

Code generation using proxies

Rocket has a module called proxies which contain some functions for generating callable objects from IDL's. The Proxy class represents a namespace. It then generatescode representing 'get' or 'post', as found in FUNCTIONS, and attaches them to the Proxy classes. This is how Rocket maps particular funcitons into an API's namespace.

During Rocket's __init__() process, it calls generate_proxies(FUNCTIONS) and receives back a map of Proxy classes, each with get() or post() functions attached to them, as describes in FUNCTIONS. These proxy classes are then attached to our Rocket and we now have generated python code that's ready for use.

The Rocket itself is what maps this data into http calls. Becaues of this, to implement a remote API is to implement a Rocket. A use then instantiates your implementation and uses the generated functions from your implementation's FUNCTIONS list.

See rocket.proxies or Rocket.__init__() for more details.

Http handling

Rocket's module contains a few functions for handling rocket's http interactions. The main function here is urlread() which takes some arguments for tweaking the call, like which http method (GET, POST, DELETE) to use or if basic_auth is turned on.

Functionality for file handling will be in there soon but is not complete.


Auth currently contains some functions for signing API requests and basic_auth. For request signatures, sign_args and sign_sorted_values are available. Often enough a timestamp can be used to limit the lifespan of the signature.

sign_args takes the request arguments, the secret key and a hashing algorithm (defaults to md5). This algorithm concatenates strings of the arguments, like arg1=val1arg2=val2, and generates the key like:

# get string of args like 'arg1=val1arg2=val2'
s = _join_kv_pairs(args, hash_alg=hash_alg)
# note: this algorithm *postfixes* s with the key
hash_input = s + api_secret_key
return hash_alg(hash_input).hexdigest()

sign_sorted_values is similar, but it's signature string is a sorted list of the request's values, like 'avalue1value2zebra1' and prefixes this string with the secret key for it's signature.

Each API is different. :)

# extact flattened list of values found in args
values = _extract_param_values(args)
arranged_args = sorted(values)
s = ''.join(arranged_args)
# note: this algorithm *prefixes* s with the key
hash_input = api_secret_key + s
return hash_alg(hash_input).hexdigest()

Install It

python ./ install

pip / easy_install support on the way


James Dennis <>

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