Python API Client

A client for communicating with an api should be a clean abstraction over the third part api you are communicating with. It should be easy to understand and have the sole responsibility of calling the endpoints and returning data.

To achieve this, APIClient takes care of the other (often duplicated) responsibilities, such as authentication and response handling, moving that code away from the clean abstraction you have designed.

Quick links

1. Installation
2. Client in action
3. Adding retries to requests
4. Working with paginated responses
5. Authenticating your requests
6. Handling the formats of your responses
7. Correctly encoding your outbound request data
8. Handling bad requests and responses
9. Endpoints as code
10. Extensions

Installation

pip install api-client

Usage

Simple Example

from apiclient import APIClient

class MyClient(APIClient):

    def list_customers(self):
        url = "http://example.com/customers"
        return self.get(url)

    def add_customer(self, customer_info):
        url = "http://example.com/customers"
        return self.post(url, data=customer_info)

>>> client = MyClient()
>>> client.add_customer({"name": "John Smith", "age": 28})
>>> client.list_customers()
[
    ...,
    {"name": "John Smith", "age": 28},
]

The APIClient exposes a number of predefined methods that you can call This example uses get to perform a GET request on an endpoint. Other methods include: post, put, patch and delete. More information on these methods is documented in the Interface.

For a more complex use case example, see: Extended example

Retrying

To add some robustness to your client, the power of tenacity has been harnessed to add a @retry_request decorator to the apiclient toolkit.

This will retry any request which responds with a 5xx status_code (which is normally safe to do as this indicates something went wrong when trying to make the request), or when an UnexpectedError occurs when attempting to establish the connection.

@retry_request has been configured to retry for a maximum of 5 minutes, with an exponential backoff strategy. For more complicated uses, the user can use tenacity themselves to create their own custom decorator.

Usage:

from apiclient import retry_request

class MyClient(APIClient):

    @retry_request
    def retry_enabled_method():
        ...

For more complex use cases, you can build your own retry decorator using tenacity along with the custom retry strategy.

For example, you can build a retry decorator that retries APIRequestError which waits for 2 seconds between retries and gives up after 5 attempts.

import tenacity
from apiclient.retrying import retry_if_api_request_error

retry_decorator = tenacity.retry(
    retry=retry_if_api_request_error(),
    wait=tenacity.wait_fixed(2),
    stop=tenacity.stop_after_attempt(5),
    reraise=True,
)

Or you can build a decorator that will retry only on specific status codes (following a failure).

retry_decorator = tenacity.retry(
    retry=retry_if_api_request_error(status_codes=[500, 501, 503]),
    wait=tenacity.wait_fixed(2),
    stop=tenacity.stop_after_attempt(5),
    reraise=True,
)

Pagination

In order to support contacting pages that respond with multiple pages of data when making get requests, add a @paginated decorator to your client method. @paginated can paginate the requests either where the pages are specified in the query parameters, or by modifying the url.

Usage is simple in both cases; paginator decorators take a Callable with two required arguments:

• by_query_params -> callable takes response and previous_page_params.
• by_url -> callable takes respones and previous_page_url. The callable will need to return either the params in the case of by_query_params, or a new url in the case of by_url. If the response is the last page, the function should return None.

Usage:

from apiclient import paginated


def next_page_by_params(response, previous_page_params):
    # Function reads the response data and returns the query param
    # that tells the next request to go to.
    return {"next": response["pages"]["next"]}


def next_page_by_url(response, previous_page_url):
    # Function reads the response and returns the url as string
    # where the next page of data lives.
    return response["pages"]["next"]["url"]


class MyClient(APIClient):

    @paginated(by_query_params=next_page_by_params)
    def paginated_example_one():
        ...

    @paginated(by_url=next_page_by_url)
    def paginated_example_two():
        ...

Authentication Methods

Authentication methods provide a way in which you can customize the client with various authentication schemes through dependency injection, meaning you can change the behaviour of the client without changing the underlying implementation.

The apiclient supports the following authentication methods, by specifying the initialized class on initialization of the client, as follows:

client = ClientImplementation(
   authentication_method=(),
   response_handler=...,
   request_formatter=...,
)

NoAuthentication

This authentication method simply does not add anything to the client, allowing the api to contact APIs that do not enforce any authentication.

Example:

client = ClientImplementation(
   authentication_method=NoAuthentication(),
   response_handler=...,
   request_formatter=...,
)

QueryParameterAuthentication

This authentication method adds the relevant parameter and token to the client query parameters. Usage is as follows:

client = ClientImplementation(
    authentication_method=QueryParameterAuthentication(parameter="apikey", token="secret_token"),
    response_handler=...,
    request_formatter=...,
)

Example. Contacting a url with the following data

http://api.example.com/users?age=27

Will add the authentication parameters to the outgoing request:

http://api.example.com/users?age=27&apikey=secret_token

HeaderAuthentication

This authentication method adds the relevant authorization header to the outgoing request. Usage is as follows:

client = ClientImplementation(
    authentication_method=HeaderAuthentication(token="secret_value"),
    response_handler=...,
    request_formatter=...,
)

# Constructs request header:
{"Authorization": "Bearer secret_value"}

The Authorization parameter and Bearer scheme can be adjusted by specifying on method initialization.

authentication_method=HeaderAuthentication(
   token="secret_value"
   parameter="apikey",
   scheme="Token",
)

# Constructs request header:
{"apikey": "Token secret_value"}

Or alternatively, when APIs do not require a scheme to be set, you can specify it as a value that evaluates to False to remove the scheme from the header:

authentication_method=HeaderAuthentication(
   token="secret_value"
   parameter="token",
   scheme=None,
)

# Constructs request header:
{"token": "secret_value"}

Additional header values can be passed in as a dict here when API's require more than one header to authenticate:

authentication_method=HeaderAuthentication(
   token="secret_value"
   parameter="token",
   scheme=None,
   extra={"more": "another_secret"}
)

# Constructs request header:
{"token": "secret_value", "more": "another_secret"}

BasicAuthentication

This authentication method enables specifying a username and password to APIs that require such.

client = ClientImplementation(
    authentication_method=BasicAuthentication(username="foo", password="secret_value"),
    response_handler=...,
    request_formatter=...,
)

CookieAuthentication

This authentication method allows a user to specify a url which is used to authenticate an initial request, made at APIClient initialization, with the authorization tokens then persisted for the duration of the client instance in cookie storage.

These cookies use the http.cookiejar.CookieJar() and are set on the session so that all future requests contain these cookies.

As the method of authentication at the endpoint is not standardised across API's, the authentication method can be customized using one of the already defined authentication methods; QueryParameterAuthentication, HeaderAuthentication, BasicAuthentication.

client = ClientImplementation(
    authentication_method=(
        CookieAuthentication(
            auth_url="https://example.com/authenticate",
            authentication=HeaderAuthentication("1234-secret-key"),
        ),
    response_handler=...,
    request_formatter=...,
)

Response Handlers

Response handlers provide a standard way of handling the final response following a successful request to the API. These must inherit from BaseResponseHandler and implement the get_request_data() method which will take the requests.Response object and parse the data accordingly.

The apiclient supports the following response handlers, by specifying the class on initialization of the client as follows:

The response handler can be omitted, in which case no formatting is applied to the outgoing data.

client = ClientImplementation(
   authentication_method=...,
   response_handler=,
   request_formatter=...,
)

RequestsResponseHandler

Handler that simply returns the original Response object with no alteration.

Example:

client = ClientImplementation(
    authentication_method=...,
    response_handler=RequestsResponseHandler,
    request_formatter=...,
)

JsonResponseHandler

Handler that parses the response data to json and returns the dictionary. If an error occurs trying to parse to json then a UnexpectedError will be raised.

Example:

client = ClientImplementation(
    authentication_method=...,
    response_handler=JsonResponseHandler,
    request_formatter=...,
)

XmlResponseHandler

Handler that parses the response data to an xml.etree.ElementTree.Element. If an error occurs trying to parse to xml then a UnexpectedError will be raised.

Example:

client = ClientImplementation(
    authentication_method=...,
    response_handler=XmlResponseHandler,
    request_formatter=...,
)

Request Formatters

Request formatters provide a way in which the outgoing request data can be encoded before being sent, and to set the headers appropriately.

These must inherit from BaseRequestFormatter and implement the format() method which will take the outgoing data object and format accordingly before making the request.

The apiclient supports the following request formatters, by specifying the class on initialization of the client as follows:

client = ClientImplementation(
   authentication_method=...,
   response_handler=...,
   request_formatter=,
)

JsonRequestFormatter

Formatter that converts the data into a json format and adds the application/json Content-type header to the outgoing requests.

Example:

client = ClientImplementation(
    authentication_method=...,
    response_handler=...,
    request_formatter=JsonRequestFormatter,
)

Exceptions

The exception handling for api-client has been designed in a way so that all exceptions inherit from one base exception type: APIClientError. From there, the exceptions have been broken down into the following categories:

ResponseParseError

Something went wrong when trying to parse the successful response into the defined format. This could be due to a misuse of the ResponseHandler, i.e. configuring the client with an XmlResponseHandler instead of a JsonResponseHandler

APIRequestError

Something went wrong when making the request. These are broken down further into the following categories to provide greater granularity and control.

RedirectionError

A redirection status code (3xx) was returned as a final code when making the request. This means that no data can be returned to the client as we could not find the requested resource as it had moved.

ClientError

A clienterror status code (4xx) was returned when contacting the API. The most common cause of these errors is misuse of the client, i.e. sending bad data to the API.

ServerError

The API was unreachable when making the request. I.e. a 5xx status code.

UnexpectedError

An unexpected error occurred when using the client. This will typically happen when attempting to make the request, for example, the client never receives a response. It can also occur to unexpected status codes (>= 600).

Custom Error Handling

Error handlers allow you to customize the way request errors are handled in the application.

Create a new error handler, extending BaseErrorHandler and implement the get_exception static method.

Pass the custom error handler into your client upon initialization.

Example:

from apiclient.error_handlers import BaseErrorHandler
from apiclient import exceptions
from apiclient.response import Response

class MyErrorHandler(BaseErrorHandler):

    @staticmethod
    def get_exception(response: Response) -> exceptions.APIRequestError:
        """Parses client errors to extract bad request reasons."""
        if 400 <= response.get_status_code() < 500:
            json = response.get_json()
            return exceptions.ClientError(json["error"]["reason"])
        
        return exceptions.APIRequestError("something went wrong")
        

In the above example, you will notice that we are utilising an internal Response object. This has been designed to abstract away the underlying response returned from whatever strategy that you are using. The Response contains the following methods:

• get_original: returns the underlying response object. This has been implemented for convenience and shouldn't be relied on.
• get_status_code: returns the integer status code.
• get_raw_data: returns the textual data from the response.
• get_json: should return the json from the response.
• get_status_reason: returns the reason for any HTTP error code.
• get_requested_url: returns the url that the client was requesting.

Request Strategy

The design of the client provides a stub of a client, exposing the required methods; get, post, etc. And this then calls the implemented methods of a request strategy.

This allows us to swap in/out strategies when needed. I.e. you can write your own strategy that implements a different library (e.g. urllib). Or you could pass in a mock strategy for testing purposes.

Example strategy for testing:

from unittest.mock import Mock

from apiclient import APIClient
from apiclient.request_strategies import BaseRequestStrategy

def test_get_method():
    """test that the get method is called on the underlying strategy.
    
    This does not execute any external HTTP call.
    """
    mock_strategy = Mock(spec=BaseRequestStrategy)
    client = APIClient(request_strategy=mock_strategy)
    client.get("http://google.com")
    mock_strategy.get.assert_called_with("http://google.com", params=None)

Endpoints

The apiclient also provides a convenient way of defining url endpoints with use of the @endpoint decorator. In order to decorate a class with @endpoint the decorated class must define a base_url attribute along with the required resources. The decorator will combine the base_url with the resource.

Example:

from apiclient import endpoint

@endpoint(base_url="http://foo.com")
class Endpoint:
    resource = "search"

>>> Endpoint.resource
"http://foo.com/search"

Extensions

Marshalling JSON

api-client-jsonmarshal: automatically marshal to/from JSON into plain python dataclasses. Full usage examples can be found in the extensions home page.

Pydantic

api-client-pydantic: validate request data and converting json straight to pydantic class.

Extended Example

from apiclient import (
    APIClient,
    endpoint,
    paginated,
    retry_request,
    HeaderAuthentication,
    JsonResponseHandler,
    JsonRequestFormatter,
)
from apiclient.exceptions import APIClientError

# Define endpoints, using the provided decorator.
@endpoint(base_url="https://jsonplaceholder.typicode.com")
class Endpoint:
    todos = "todos"
    todo = "todos/{id}"


def get_next_page(response):
    return {
        "limit": response["limit"],
        "offset": response["offset"] + response["limit"],
    }


# Extend the client for your API integration.
class JSONPlaceholderClient(APIClient):

    @paginated(by_query_params=get_next_page)
    def get_all_todos(self) -> dict:
        return self.get(Endpoint.todos)

    @retry_request
    def get_todo(self, todo_id: int) -> dict:
        url = Endpoint.todo.format(id=todo_id)
        return self.get(url)


# Initialize the client with the correct authentication method,
# response handler and request formatter.
>>> client = JSONPlaceholderClient(
    authentication_method=HeaderAuthentication(token=""),
    response_handler=JsonResponseHandler,
    request_formatter=JsonRequestFormatter,
)


# Call the client methods.
>>> client.get_all_todos()
[
    {
        'userId': 1,
        'id': 1,
        'title': 'delectus aut autem',
        'completed': False
    },
    ...,
    {
        'userId': 10,
        'id': 200,
        'title': 'ipsam aperiam voluptates qui',
        'completed': False
    }
]


>>> client.get_todo(45)
{
    'userId': 3,
    'id': 45,
    'title': 'velit soluta adipisci molestias reiciendis harum',
    'completed': False
}


# REST APIs correctly adhering to the status codes to provide meaningful
# responses will raise the appropriate exeptions.
>>> client.get_todo(450)
# NotFound: 404 Error: Not Found for url: https://jsonplaceholder.typicode.com/todos/450

>>> try:
...     client.get_todo(450)
... except APIClientError:
...     print("All client exceptions inherit from APIClientError")
"All client exceptions inherit from APIClientError"

APIClient Interface

The APIClient provides the following public interface:

• post(self, endpoint: str, data: dict, params: OptionalDict = None)

  Delegate to POST method to send data and return response from endpoint.

• get(endpoint: str, params: OptionalDict = None)

  Delegate to GET method to get response from endpoint.

• put(endpoint: str, data: dict, params: OptionalDict = None)

  Delegate to PUT method to send and overwrite data and return response from endpoint.

• patch(endpoint: str, data: dict, params: OptionalDict = None)

  Delegate to PATCH method to send and update data and return response from endpoint

• delete(endpoint: str, params: OptionalDict = None)

  Delegate to DELETE method to remove resource located at endpoint.

• get_request_timeout() -> float

  By default, all requests have been set to have a default timeout of 10.0 s. This is to avoid the request waiting forever for a response, and is recommended to always be set to a value in production applications. It is however possible to override this method to return the timeout required by your application.

Mentions

Many thanks to JetBrains for supplying me with a license to use their product in the development of this tool.