.. _serialization: Serialization ************* Various serialization formats exist for transmitting structured data over the network: JSON is a popular choice amongst many public APIs partly because its human readable, while a more compact format, such as `Protocol Buffers `_, may be more appropriate for a private API used within an organization. Regardless what serialization format your API uses, Uplink -- with a little bit of help -- can automatically decode responses and encode request bodies to and from Python objects using the selected format. This neatly abstracts the HTTP layer from your API client, so callers can operate on objects that make sense to your model instead of directly dealing with the underlying protocol. This document walks you through how to leverage Uplink's serialization support, including integrations for third-party serialization libraries like :mod:`marshmallow`, :mod:`pydantic` and tools for writing custom conversion strategies that fit your unique needs. .. _using_marshmallow_schemas: Using Marshmallow Schemas ========================= :mod:`marshmallow` is a framework-agnostic, object serialization library for Python. Uplink comes with built-in support for Marshmallow; you can integrate your Marshmallow schemas with Uplink for easy JSON (de)serialization. First, create a :class:`marshmallow.Schema`, declaring any necessary conversions and validations. Here's a simple example: .. code-block:: python import marshmallow class RepoSchema(marshmallow.Schema): full_name = marshmallow.fields.Str() @marshmallow.post_load def make_repo(self, data): owner, repo_name = data["full_name"].split("/") return Repo(owner=owner, name=repo_name) Then, specify the schema using the :class:`@returns ` decorator: .. code-block:: python :emphasize-lines: 2 class GitHub(Consumer): @returns(RepoSchema(many=True)) @get("users/{username}/repos") def get_repos(self, username): """Get the user's public repositories.""" Python 3 users can use a return type hint instead: .. code-block:: python :emphasize-lines: 3 class GitHub(Consumer): @get("users/{username}/repos") def get_repos(self, username) -> RepoSchema(many=True) """Get the user's public repositories.""" Your consumer should now return Python objects based on your Marshmallow schema: .. code-block:: python github = GitHub(base_url="https://api.github.com") print(github.get_repos("octocat")) # Output: [Repo(owner="octocat", name="linguist"), ...] For a more complete example of Uplink's :mod:`marshmallow` support, check out `this example on GitHub `_. .. _using_pydantic_schemas: Using Pydantic Models ========================= :mod:`pydantic` is a framework-agnostic, object serialization library for Python >= 3.6. Uplink comes with built-in support for Pydantic; you can integrate your Pydantic models with Uplink for easy JSON (de)serialization. First, create a :class:`pydantic.BaseModel`, declaring any necessary conversions and validations. Here's a simple example: .. code-block:: python from typing import List from pydantic import BaseModel, HttpUrl class Owner(BaseModel): id: int avatar_url: HttpUrl organizations_url: HttpUrl class Repo(BaseModel): id: int full_name: str owner: Owner Then, specify the schema using the :class:`@returns ` decorator: .. code-block:: python :emphasize-lines: 2 class GitHub(Consumer): @returns.json(List[Repo]) @get("users/{username}/repos") def get_repos(self, username): """Get the user's public repositories.""" Python 3 users can use a return type hint instead: .. code-block:: python :emphasize-lines: 3 class GitHub(Consumer): @returns.json() @get("users/{username}/repos") def get_repos(self, username) -> List[Repo]: """Get the user's public repositories.""" Your consumer should now return Python objects based on your Pydantic model: .. code-block:: python github = GitHub(base_url="https://api.github.com") print(github.get_repos("octocat")) # Output: [User(id=132935648, full_name='octocat/boysenberry-repo-1', owner=Owner(...), ...] .. note:: You may have noticed the usage of `returns.json` in both examples. Unlike :mod:`marshmallow`, :mod:`pydantic` has no `many` parameter to control the deserialization of multiple objects. The recommended approach is to use `returns.json` instead of defining a new model with a `__root__` element. Serializing Method Arguments ============================ Most method argument annotations like :class:`~uplink.Field` and :class:`~uplink.Body` accept a :obj:`type` parameter that specifies the method argument's expected type or schema, for the sake of serialization. For example, following the :mod:`marshmallow` example from above, we can specify the :class:`RepoSchema` as the :obj:`type` of a :class:`~uplink.Body` argument: .. code-block:: python from uplink import Consumer, Body class GitHub(Consumer): @json @post("user/repos") def create_repo(self, repo: Body(type=RepoSchema)): """Creates a new repository for the authenticated user.""" Then, the :obj:`repo` argument should accept instances of :class:`Repo`, to be serialized appropriately using the :class:`RepoSchema` with Uplink's :mod:`marshmallow` integration (see :ref:`using_marshmallow_schemas` for the full setup). .. code-block:: python repo = Repo(name="my_favorite_new_project") github.create_repo(repo) The sample code above using :mod:`marshmallow` is also reproducible using :mod:`pydantic`: .. code-block:: python from uplink import Consumer, Body class CreateRepo(BaseModel): name: str delete_branch_on_merge: bool class GitHub(Consumer): @post("user/repos") def create_repo(self, repo: Body(type=CreateRepo)): """Creates a new repository for the authenticated user.""" Then, calling the client. .. code-block:: python repo = CreateRepo(name="my-new-uplink-pydantic", delete_branch_on_merge=True) github.create_repo(repo) .. _custom_json_deserialization: Custom JSON Conversion ====================== Recognizing JSON's popularity amongst public APIs, Uplink provides some out-of-the-box utilities that make adding JSON serialization support for your objects simple. Deserialization --------------- :class:`@returns.json ` is handy when working with APIs that provide JSON responses. As its leading positional argument, the decorator accepts a class that represents the expected schema of the JSON response body: .. code-block:: python :emphasize-lines: 2 class GitHub(Consumer): @returns.json(User) @get("users/{username}") def get_user(self, username): pass Python 3 users can alternatively use a return type hint: .. code-block:: python :emphasize-lines: 4 class GitHub(Consumer): @returns.json @get("users/{username}") def get_user(self, username) -> User: pass Next, if your objects (e.g., :py:obj:`User`) are not defined using a library for which Uplink has built-in support (such as :py:mod:`marshmallow`), you will also need to register a converter that tells Uplink how to convert the HTTP response into your expected return type. To this end, we can use :py:meth:`@loads.from_json ` to define a simple JSON reader for :class:`User`: .. code-block:: python from uplink import loads @loads.from_json(User) def user_json_reader(user_cls, json): return user_cls(json["id"], json["username"]) The decorated function, :py:func:`user_json_reader`, can then be passed into the :py:attr:`converter` constructor parameter when instantiating a :py:class:`uplink.Consumer` subclass: .. code-block:: python github = GitHub(base_url=..., converter=user_json_reader) Alternatively, you can add the :py:func:`@uplink.install ` decorator to register the converter function as a default converter, meaning the converter will be included automatically with any consumer instance and doesn't need to be explicitly provided through the :py:obj:`converter` parameter: .. code-block:: python :emphasize-lines: 1 from uplink import loads, install @install @loads.from_json(User) def user_json_reader(user_cls, json): return user_cls(json["id"], json["username"]) At last, calling the :meth:`GitHub.get_user` method should now return an instance of our :class:`User` class: .. code-block:: python github.get_user("octocat") # Output: [User(id=583231, name="The Octocat"), ...] Serialization ------------- :class:`@json ` is a decorator for :class:`~uplink.Consumer` methods that send JSON requests. Using this decorator requires annotating your arguments with either :class:`~uplink.Field` or :class:`~uplink.Body`. Both annotations support an optional :obj:`type` argument for the purpose of serialization: .. code-block:: python :emphasize-lines: 6 from uplink import Consumer, Body class GitHub(Consumer): @json @post("user/repos") def create_repo(self, user: Body(type=Repo)): """Creates a new repository for the authenticated user.""" Similar to deserialization case, we must register a converter that tells Uplink how to turn the :py:obj:`Repo` object to JSON, since the class is not defined using a library for which Uplink has built-in support (such as :py:mod:`marshmallow`). To this end, we can use :py:meth:`@dumps.to_json ` to define a simple JSON writer for :class:`Repo`: .. code-block:: python from uplink import dumps @dumps.to_json(Repo) def repo_json_writer(repo_cls, repo): return {"name": repo.name, "private": repo.is_private()} The decorated function, :py:func:`repo_json_writer`, can then be passed into the :py:attr:`converter` constructor parameter when instantiating a :py:class:`uplink.Consumer` subclass: .. code-block:: python github = GitHub(base_url=..., converter=repo_json_writer) Alternatively, you can add the :py:func:`@uplink.install ` decorator to register the converter function as a default converter, meaning the converter will be included automatically with any consumer instance and doesn't need to be explicitly provided through the :py:obj:`converter` parameter: .. code-block:: python :emphasize-lines: 1 from uplink import loads, install @install @dumps.to_json(Repo) def repo_json_writer(user_cls, json): return {"name": repo.name, "private": repo.is_private()} Now, we should be able to invoke the :meth:`GitHub.create_repo` method with an instance of :class:`Repo`: .. code-block:: python repo = Repo(name="my_new_project", private=True) github.create_repo(repo) .. _converting_collections: Converting Collections ====================== Data-driven web applications, such as social networks and forums, devise a lot of functionality around large queries on related data. Their APIs normally encode the results of these queries as collections of a common **type**. Examples include a curated feed of **posts** from subscribed accounts, the top **restaurants** in your area, upcoming *tasks** on a checklist, etc. You can use the other strategies in this section to add serialization support for a specific type, such as a **post** or a **restaurant**. Once added, this support automatically extends to collections of that type, such as sequences and mappings. For example, consider a hypothetical Task Management API that supports adding tasks to one or more user-created checklists. Here's the JSON array that the API returns when we query pending tasks on a checklist titled "home": .. code-block:: json [ { "id": 4139 "name": "Groceries" "due_date": "Monday, September 3, 2018 10:00:00 AM PST" }, { "id": 4140 "name": "Laundry" "due_date": "Monday, September 3, 2018 2:00:00 PM PST" } ] In this example, the common type could be modeled in Python as a :class:`~collections.namedtuple`, which we'll name :class:`Task`: .. code-block:: python Task = collections.namedtuple("Task", ["id", "name", "due_date"]) Next, to add JSON deserialization support for this type, we could create a custom converter using the :meth:`@loads.from_json ` decorator, which is a strategy covered in the subsection :ref:`custom_json_deserialization`. For the sake of brevity, I'll omit the implementation here, but you can follow the link above for details. Notably, Uplink lets us leverage the added support to also handle collections of type :class:`Task`. The :mod:`uplink.types` module exposes two collection types, :data:`~uplink.List` and :data:`~uplink.types.Dict`, to be used as function return type annotations. In our example, the query for pending tasks returns a list: .. code-block:: python :emphasize-lines: 6 from uplink import Consumer, returns, get, types class TaskApi(Consumer): @returns.json @get("tasks/{checklist}?due=today") def get_pending_tasks(self, checklist) -> types.List[Task] If you are a Python 3.5+ user that is already leveraging the :mod:`typing` module to support type hints as specified by :pep:`484` and :pep:`526`, you can safely use :class:`typing.List` and :class:`typing.Dict` here instead of the annotations from :mod:`uplink.types`: .. code-block:: python :emphasize-lines: 7 import typing from uplink import Consumer, returns, get class TaskApi(Consumer): @returns.json @get("tasks/{checklist}?due=today") def get_pending_tasks(self, checklist) -> typing.List[Task] Now, the consumer can handle these queries with ease: .. code-block:: python >>> task_api.get_pending_tasks("home") [Task(id=4139, name='Groceries', due_date='Monday, September 3, 2018 10:00:00 AM PST'), Task(id=4140, name='Laundry', due_date='Monday, September 3, 2018 2:00:00 PM PST')] Note that this feature works with any serialization format, not just JSON. Writing A Custom Converter ========================== Extending Uplink's support for other serialization formats or libraries (e.g., XML, Thrift, Avro) is pretty straightforward. When adding support for a new serialization library, create a subclass of :class:`converters.Factory `, which defines abstract methods for different serialization scenarios (deserializing the response body, serializing the request body, etc.), and override each relevant method to return a callable that handles the method's corresponding scenario. For example, a factory that adds support for Python's :mod:`pickle` protocol could look like: .. code-block:: python import pickle from uplink import converters class PickleFactory(converters.Factory): """Adapter for Python's Pickle protocol.""" def create_response_body_converter(self, cls, request_definition): # Return callable to deserialize response body into Python object. return lambda response: pickle.loads(response.content) def create_request_body_converter(self, cls, request_definition): # Return callable to serialize Python object into bytes. return pickle.dumps Then, when instantiating a new consumer, you can supply this implementation through the ``converter`` constructor argument of any :class:`Consumer` subclass: .. code-block:: python client = MyApiClient(BASE_URL, converter=PickleFactory()) If the added support should apply broadly, you can alternatively decorate your :class:`converters.Factory ` subclass with the :meth:`@uplink.install ` decorator, which ensures that Uplink automatically adds the factory to new instances of any :class:`Consumer` subclass. This way you don't have to explicitly supply the factory each time you instantiate a consumer. .. code-block:: python :emphasize-lines: 3 from uplink import converters, install @install class PickleFactory(converters.Factory): ... For a concrete example of extending support for a new serialization format or library with this approach, checkout `this Protobuf extension `_ for Uplink.