Quickstart

Ready to write your first API client with Uplink? This guide will walk you through what you’ll need to know to get started.

First, make sure you’ve installed (or updated) Uplink:

$ pip install -U uplink

Defining an API Client

Writing a structured API client with Uplink is very simple.

To start, create a subclass of Consumer. For example, here’s the beginning of our GitHub client (we’ll add some methods to this class soon):

from uplink import Consumer

class GitHub(Consumer):
   ...

When creating an instance of this consumer, we can use the base_url constructor argument to identify the target service. In our case, it’s GitHub’s public API:

github = GitHub(base_url="https://api.github.com/")

Note

base_url is especially useful for creating clients that target separate services with similar APIs; for example, we could use this GitHub consumer to also create clients for any GitHub Enterprise instance for projects hosted outside of the public GitHub.com service. Another example is creating separate clients for a company’s production and staging environments, which are typically hosted on separate domains but expose the same API.

So far, this class looks like any other Python class. The real magic happens when you define methods to interact with the webservice using Uplink’s HTTP method decorators, which we cover next.

Making a Request

With Uplink, making a request to a webservice is as simple as invoking a method.

Any method of a Consumer subclass can be decorated with one of Uplink’s HTTP method decorators: @get, @post, @put, @patch, @head, and @delete:

class GitHub(Consumer):
    @get("repositories")
    def get_repos(self):
        """List all public repositories."""

As shown above, the method’s body can be left empty.

The decorator’s first argument is the resource endpoint: i.e., the relative path from base_url, which we covered above:

@get("repositories")

Note

To build a request’s absolute URL, Uplink resolves the relative path against the Consumer’s base url using urljoin, which implements the RFC 3986 standards. For a simplified overview of these standards, see these recommendations and examples from Retrofit’s documentation.

You can also specify query parameters:

@get("repositories?since=364")

Finally, invoke the method to send a request:

>>> github = GitHub(base_url="https://api.github.com/")
>>> github.get_repos()
<Response [200]>
>>> _.url
https://api.github.com/repositories

By default, uplink uses Requests, so the response we get back from GitHub is wrapped inside a requests.Response instance. (If you want, you can swap out Requests for a different backing HTTP client, such as aiohttp.)

URL Manipulation

Resource endpoints can include URI template parameters that depend on method arguments. A simple URI parameter is an alphanumeric string surrounded by { and }.

To match the parameter with a method argument, either match the argument’s name with the alphanumeric string, like so:

@get("users/{username}")
def get_user(self, username): pass

or use the Path annotation.

@get("users/{username}")
def get_user(self, name: Path("username")): pass

Query parameters can also be added dynamically by method arguments.

@get("users/{username}/repos")
def get_repos(self, username, sort: Query): pass

Setting a default value for the query parameter works like you’d expect it to:

@get("users/{username}/repos")
def get_repos(self, username, sort: Query = "created"): pass

To make the query parameter optional, set the argument’s default value to None. Then, if the argument is not specified at runtime, the parameter will not appear in the request.

@get("users/{username}/repos")
def get_repos(self, username, sort: Query = None): pass

Useful for “catch-all” or complex query parameter combinations, the QueryMap annotation accepts a mapping of query parameters:

@get("users/{username}/repos")
def get_repos(self, username, **options: QueryMap): pass

You can set static query parameters for a method using the @params decorator.

@params({"client_id": "my-client", "client_secret": "****"})
@get("users/{username}")
def get_user(self, username): pass

@params can be used as a class decorator for query parameters that need to be included with every request:

@params({"client_id": "my-client", "client_secret": "****"})
class GitHub(Consumer):
    ...

Header Manipulation

You can set static headers for a method using the @headers decorator.

@headers({
    "Accept": "application/vnd.github.v3.full+json",
    "User-Agent": "Uplink-Sample-App"
})
@get("users/{username}")
def get_user(self, username): pass

@headers can be used as a class decorator for headers that need to be added to every request:

@headers({
    "Accept": "application/vnd.github.v3.full+json",
    "User-Agent": "Uplink-Sample-App"
})
class GitHub(Consumer):
    ...

A request header can depend on the value of a method argument by using the Header function parameter annotation:

@get("user")
def get_user(self, authorization: Header("Authorization"):
    """Get an authenticated user."""

Request Body

The Body annotation identifies a method argument as the the HTTP request body:

@post("user/repos")
def create_repo(self, repo: Body): pass

This annotation works well with the keyword arguments parameter (denoted by the ** prefix):

@post("user/repos")
def create_repo(self, **repo_info: Body): pass

Moreover, this annotation is useful when using supported serialization formats, such as JSON and Protocol Buffers. Take a look at this guide for more about serialization with Uplink.

Form Encoded, Multipart, and JSON Requests

Methods can also be declared to send form-encoded, multipart, and JSON data.

Form-encoded data is sent when @form_url_encoded decorates the method. Each key-value pair is annotated with a Field annotation:

@form_url_encoded
@patch("user")
def update_user(self, name: Field, email: Field): pass

Multipart requests are used when @multipart decorates the method. Parts are declared using the Part annotation:

@multipart
@put("user/photo")
def upload_photo(self, photo: Part, description: Part): pass

JSON data is sent when @json decorates the method. The Body annotation declares the JSON payload:

@json
@patch("user")
def update_user(self, **user_info: uplink.Body):
    """Update an authenticated user."""

Alternatively, the Field annotation declares a JSON field:

@json
@patch("user")
def update_user_bio(self, bio: Field):
    """Update the authenticated user's profile bio."""

Handling JSON Responses

Many modern public APIs serve JSON responses to their clients.

If your Consumer subclass accesses a JSON API, you can decorate any method with @returns.json to directly return the JSON response, instead of a response object, when invoked:

class GitHub(Consumer):
    @returns.json
    @get("users/{username}")
    def get_user(self, username):
        """Get a single user."""
>>> github = GitHub("https://api.github.com")
>>> github.get_user("prkumar")
{'login': 'prkumar', 'id': 10181244, ...

You can also target a specific field of the JSON response by using the decorator’s key argument to select the target JSON field name:

class GitHub(Consumer):
    @returns.json(key="blog")
    @get("users/{username}")
    def get_blog_url(self, username):
        """Get the user's blog URL."""
>>> github.get_blog_url("prkumar")
"https://prkumar.io"

Note

JSON responses may represent existing Python classes in your application (for example, a GitHubUser). Uplink supports this kind of conversion (i.e., deserialization), and we detail this support in the next guide.

Persistence Across Requests from a Consumer

The session property of a Consumer instance exposes the instance’s configuration and allows for the persistence of certain properties across requests sent from that instance.

You can provide default headers and query parameters for requests sent from a consumer instance through its session property, like so:

class GitHub(Consumer):

    def __init__(self, base_url, username, password):
        super(GitHub, self).__init__(base_url=base_url)

        # Creates the API token for this user
        api_key = create_api_key(username, password)

        # Send the API token as a query parameter with each request.
        self.session.params["access_token"] = api_key

    @get("user/repos")
    def get_user_repos(self, sort_by: Query("sort")):
        """Lists public repositories for the authenticated user."""

Headers and query parameters added through the session are applied to all requests sent from the consumer instance.

github = GitHub("prkumar", "****")

# Both `access_token` and `sort` are sent with the request.
github.get_user_repos(sort_by="created")

Notably, in case of conflicts, the method-level headers and parameters override the session-level, but the method-level properties are not persisted across requests.

Response and Error Handling

Sometimes, you need to validate a response before it is returned or even calculate a new return value from the response. Or, you may need to handle errors from the underlying client before they reach your users.

With Uplink, you can address these concerns by registering a callback with one of these decorators: @response_handler and @error_handler.

@response_handler registers a callback to intercept responses before they are returned (or deserialized):

def raise_for_status(response):
    """Checks whether or not the response was successful."""
    if 200 <= response.status_code < 300:
        # Pass through the response.
        return response

    raise UnsuccessfulRequest(response.url)

class GitHub(Consumer):
    @response_handler(raise_for_status)
    @post("user/repo")
    def create_repo(self, name: Field):
        """Create a new repository."""

@error_handler registers a callback to handle an exception thrown by the underlying HTTP client (e.g., requests.Timeout):

def raise_api_error(exc_type, exc_val, exc_tb):
    """Wraps client error with custom API error"""
    raise MyApiError(exc_val)

class GitHub(Consumer):
    @error_handler(raise_api_error)
    @post("user/repo")
    def create_repo(self, name: Field):
        """Create a new repository."""

To apply a handler onto all methods of a Consumer subclass, you can simply decorate the class itself:

@error_handler(raise_api_error)
class GitHub(Consumer):
    ...

Notably, the decorators can be stacked on top of one another to chain their behaviors:

@response_handler(check_expected_headers)  # Second, check headers
@response_handler(raise_for_status)  # First, check success
class GitHub(Consumer):
    ...

Lastly, both decorators support the optional argument requires_consumer. When this option is set to True, the registered callback should accept a reference to the Consumer instance as its leading argument:

 @error_handler(requires_consumer=True)
 def raise_api_error(consumer, exc_type, exc_val, exc_tb):
     """Wraps client error with custom API error"""
     ...

 class GitHub(Consumer):
     @raise_api_error
     @post("user/repo")
     def create_repo(self, name: Field):
         """Create a new repository."""

Retrying

Networks are unreliable. Requests can fail for various reasons. In some cases, such as after a connection timeout, simply retrying a failed request is appropriate. The @retry decorator can handle this for you:

from uplink import retry, Consumer, get

class GitHub(Consumer):
   @retry
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

Without any further configuration, the decorator will retry requests that fail for any reasons. To constrain which exceptions should prompt a retry attempt, use the on_exception argument:

from uplink import retry, Consumer, get

class GitHub(Consumer):
   # Retry only on failure to connect to the remote server.
   @retry(on_exception=retry.CONNECTION_TIMEOUT)
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

Further, as long as the expected exception is thrown, the decorator will repeatedly retry until a response is rendered. If you’d like to seize retrying after a specific number of attempts, use the max_attempts argument:

from uplink import retry, Consumer, get

class GitHub(Consumer):
   # Try four times, then fail hard if no response.
   @retry(max_attempts=4)
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

The @retry decorators offers a bunch of other features! Below is a contrived example… checkout the API documentation for more:

from uplink import retry, Consumer, get

class GitHub(Consumer):
   @retry(
      # Retry on 503 response status code or any exception.
      when=retry.when.status(503) | retry.when.raises(Exception)
      # Stop after 5 attempts or when backoff exceeds 10 seconds.
      stop=retry.stop.after_attempt(5) | retry.stop.after_delay(10)
      # Use exponential backoff with added randomness.
      backoff=retry.backoff.jittered(multiplier=0.5)
   )
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

Finally, like other Uplink decorators, you can decorate a Consumer subclass with @retry to add retry support to all methods of that class.

Note

Response and error handlers (see here) are invoked after the retry condition breaks or after all retry attempts are exhausted, whatever comes first. These callbacks will receive the first response/exception that triggers the retry’s stop condition or doesn’t match its when filter.

Client-Side Rate Limiting

Often, an organization may enforce a strict limit on the number of requests a client can make to their public API within a fixed time period (e.g., 15 calls every 15 minutes) to help prevent denial-of-service (DoS) attacks and other issues caused by misbehaving clients. On the client-side, we can avoid exceeding these server-side limits by imposing our own rate limit.

The @ratelimit decorator enforces a constraint of X calls every Y seconds:

from uplink import ratelimit, Consumer, get

class GitHub(Consumer):
   @ratelimit(calls=15, period=900)  # 15 calls every 15 minutes.
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

When the consumer reaches the limit, it will wait until the next period before executing any subsequent requests. For blocking HTTP clients, such as Requests, this means the main thread is blocked until then. On the other hand, using a non-blocking client, such as aiohttp, enables you to continue making progress elsewhere while the consumer waits for the current period to lapse.

Alternatively, you can fail fast when the limit is exceeded by setting the raise_on_limit argument:

class GitHub(Consumer):
   # Raise Exception when the client exceeds the rate limit.
   @ratelimit(calls=15, period=900, raise_on_limit=Exception)
   @get("user/{username}")
   def get_user(self, username):
      """Get user by username."""

Like other Uplink decorators, you can decorate a Consumer subclass with @ratelimit to add rate limiting to all methods of that class.