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`decorest` library provides an easy to use declarative REST API client interface, where definition of the API methods using decorators automatically gives a working REST client with no additional code.

Project description

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Declarative, decorator-based REST client for Python.

Overview

decorest library provides an easy to use declarative REST API client interface, where definition of the API methods using decorators automatically produces a working REST client with no additional code. In practice the library provides only an interface to describe and interact with REST services - the actual work is done underneath by either requests (default) or httpx libraries. Backend can be selected dynamically during creation of client instance.

For example:

from decorest import RestClient, GET

class DogClient(RestClient):
    def __init__(self, *args, **kwargs):
        super(DogClient, self).__init__(*args, **kwargs)

    @GET('breed/{breed_name}/list')
    def list_subbreeds(self, breed_name):
        """List all sub-breeds"""

client = DogClient('https://dog.ceo/api')

print(client.list_subbreeds('hound'))

Installation

Using pip:

pip install decorest

Usage

Basics

For most typical cases the usage should be fairly straightforward. Simply create a subclass of decorest.RestClient and define methods, which will perform calls to the actual REST service. You can declare how each function should perform the request to the service solely using decorators attached to the method definition. The method itself is not expected to have any implementation, except maybe for a docstring.

After your API client class definition is complete, simply create an instance of it and you’re good to go. This library relies on the functionality provided by either requests or httpx libraries, which means that any valid named argument, which could be passed to a requests or httpx HTTP call can be also passed to the calls of the client methods and will be forwarded as is.

For more information checkout sample clients in examples.

Choosing backend

decorest supports currently 2 backends:

To select a specific backend, simply pass it’s name to the constructor of the client:

client = DogClient('https://dog.ceo/api', backend='httpx')

If no backend is provided, requests is used by default. The client usage is largely independent of the backend, however there some minor differences in handling streams and multipart messages, please consult tests in httpbin test suite.

Decorators

Below is a list of all supported decorators along with short explanation and examples. Some decorators can be attached to both client class as well as methods, in which case the class-level decorator is applied to all HTTP methods in that class. Furthermore, each decorator can be overridden directly during the method call by providing a named argument with name equal to the decorator name.

@GET, @PUT, @POST, @PATCH, @DELETE, @HEAD, @OPTIONS

Marks the request with a specific HTTP method and the path relative to endpoint provided as argument. The path can contain variables enclosed in curly brackets, e.g.:

@GET('breed/{breed_name}/list')
def list_subbreeds(self, breed_name):
    """List all sub-breeds"""

which will be replaced by the arguments from the method definition. These decorators apply only to methods.

@query

Adds a query parameter to the request. URL encoding will be applied to the value using urlencode, e.g.:

@GET('breed/{breed_name}/list')
@query('long_names', 'longNames')
@query('limit')
def list_subbreeds(self, breed_name, long_names, limit=100):
    """List all sub-breeds"""

This decorator can take a single string parameter, which determines the name of the method argument whose value will be added as the query argument value of the same name.

In case 2 arguments are provided, the second argument determines the actual query key name, which will be used in the request query (if for some reason it should be different than the method argument name).

Furthermore, if a default value is provided in a method declaration, it will be used whenever a value for this argument is not provided during invocation.

For example, the following invocation of the above method:

client.list_subbreeds('hound', 1)

will result in the following query:

https://dog.ceo/api/breed/hound?longNames=1&limit=100

This decorator can be added only to methods.

@form

Adds a form parameter to the request. For example:

@POST('breed')
@form('breed_name')
@form('breed_url', 'breed_wikipedia_link')
def add_breed(self, breed_name, breed_url):
    """Add sub-breed"""

This decorator can take a single string parameter, which determines the name of the method argument whose value will be added as the query argument value of the same name.

In case 2 arguments are provided, the second argument determines the actual form field name, which will be used in the request form (if for some reason it cannot be the same as the method argument name).

If a method has at least one @form decorator attached, the Content-type header value will be always set to application/x-www-form-urlencoded.

This decorator can be added only to methods.

@multipart

Adds a multipart parameter to the request. For example:

@POST('post')
@multipart('part1')
@multipart('part_2', 'part2')
@multipart('test')
def post_multipart(self, part1, part_2, test):
    """Return multipart POST data."""

The first parameter to the decorator is the name of the variable in the decorated method and at the same time the name of the part in HTTP request (which will be set in the Content-Disposition header. In case the method argument name should be different than the part name in the request, a second parameter to the decorator will determine the actual name for the part in the HTTP request.

The values for the arguments can be either strings, which will be added directly as content in the appropriate part, or tuples. In case a tuple is passed, it will be treated as a file, the same way as is treated by both backend libraries.

The above method can be thus called as follows:

f = '/tmp/test.dat'
res = client.post_multipart('TEST1', 'TEST2',
                            ('filename', open(f, 'rb'), 'text/plain'))
which will generate the following parts:
  • part part1 with content TEST1
  • part part2 with content TEST2
  • part test with content read from file /tmp/test.dat

@body

Body decorator enables to specify which of the method parameters should provide the body content to the request, e.g.:

@POST('pet')
@header('content-type', 'application/json')
@header('accept', 'application/json')
@body('pet')
def add_pet(self, pet):
    """Add a new pet to the store"""

@body decorator can take an optional argument which provides a serialization handler, which will be invoked automatically before passing the argument as body content, which can be a simple lambda or a more complex function with some logic. For example:

@POST('pet')
@header('content-type', 'application/json')
@header('accept', 'application/json')
@body('pet', lambda p: json.dumps(p))
def add_pet(self, pet):
    """Add a new pet to the store"""

The above code will automatically stringify the dictionary provided as value of ‘pet’ argument using json.dumps() function.

@on

By default the request method will not return requests response object, but the response will depend on the content type of the response.

In case the HTTP request succeeds the following results are expected:

  • response.json() if the content type of response is JSON
  • response.content if the content type is binary
  • response.text otherwise

In case the request fails, response.raise_for_status() is called and should be handled in the code.

In case another behavior is required, custom handlers can be provided for each method using lambdas or functions. The provided handler is expected to take only a single argument, which is the requests response object, e.g.:

@GET('breed/{breed_name}/list')
@header('accept', 'application/json')
@on(200, lambda r: r.json())
def list_subbreeds(self, breed_name):
    """List all sub-breeds"""

This decorator can be applied to both methods and classes, however when applied to a class the handler will be called for method which receives the provided status code.

The first argument of this decorator must be an integer. On Python 3 it also possible to pass ... (i.e. Ellipsis) object, which is equivalent to HttpStatus.ANY. Any other value passed for this argument will raise TypeError.

@content

This decorator is a shortcut for @header('content-type', ...), e.g:

@POST('pet')
@content('application/json')
@header('accept', 'application/json')
@body('pet', lambda p: json.dumps(p))
def add_pet(self, pet):
    """Add a new pet to the store"""

@accept

This decorator is a shortcut for @header('accept', ...), e.g:

@GET('breed/{breed_name}/list')
@content('application/json')
@accept('application/xml')
def list_subbreeds(self, breed_name):
    """List all sub-breeds"""

@endpoint

This decorator enables to define a default endpoint for the service, which then doesn’t have to be provided in the client constructor:

@endpoint('https://dog.ceo/api')
class DogClient(RestClient):
    """List all sub-breeds"""
    def __init__(self, endpoint=None):
        super(DogClient, self).__init__(endpoint)

The endpoint provided in the client constructor will take precedence however.

@timeout

Specifies a default timeout value (in seconds) for method or entire API.

@endpoint('https://dog.ceo/api')
@timeout(5)
class DogClient(RestClient):
    """List all sub-breeds"""
    def __init__(self, endpoint=None):
        super(DogClient, self).__init__(endpoint)

@stream

This decorator allows to specify a method which returns binary stream of data. Adding this decorator to a method will add a stream=True argument to the requests call and will by default return entire requests object which then can be accessed for instance using iter_content() method.

...

class MyClient(RestClient):
    ...

    @GET('stream/{n}/{m}')
    @stream
    @query('size')
    @query('offset', 'off')
    def stream(self, n, m, size, offset):
        """Get data range"""

...

with client.stream(2,4, 1024, 200) as r:
    for b in r.iter_content(chunk_size=100):
        content.append(b)

Sessions

Based on the functionality provided by requests library in the form of session objects, sessions can significantly improve the performance of the client in case multiple responses are performed as well as maintain certain information between requests such as session cookies.

Sessions in decorest can either be created and closed manually:

s = client._session()
s.list_subbreeds('hound')
s.list_subbreeds('husky')
s._close()

or can be used via the context manager with operator:

with client._session() as s:
    s.list_subbreeds('hound')
    s.list_subbreeds('husky')

All session specific methods begin with a single underscore, in order not to interfere with any possible API method names defined in the base client class.

If some additional customization of the session is required, the underlying requests session object can be retrieved from decorest session object using _requests_session attribute:

with client._session() as s:
    s._requests_session.verify = '/path/to/cert.pem'
    s.list_subbreeds('hound')
    s.list_subbreeds('husky')

Authentication

Since authentication is highly specific to actual invocation of the REST API, and not to it’s specification, there is not decorator for authentication, but instead an authentication object (compatible with requests_ authentication mechanism) can be set in the client object using _set_auth() method, for example:

client._set_auth(HTTPBasicAuth('user', 'password'))
with client._session() as s:
    s._requests_session.verify = '/path/to/cert.pem'
    s.list_subbreeds('hound')
    s.list_subbreeds('husky')

The authentication object will be used in both regular API calls, as well as when using sessions.

Error handling

Due to the fact, that this library supports multiple HTTP backends, exceptions should be caught through a wrapper class, decorest.HTTPErrorWrapper, which contains the original exception raised by the underlying backend.

try:
    res = client.update_pet(json.dumps({'id': pet_id, 'status': 'sold'}))
except HTTPErrorWrapper as e:
    # Print original error message
    print(e.response.text)
    # Reraise the original exception
    raise e.wrapped

Grouping API methods

For larger API’s it can be useful to be able to split the API definition into multiple files but still use it from a single instance in the code.

This can be achieved by creating separate client classes for each group of operations and then create a common class, which inherits from all the group clients and provides entire API from one instance.

For example of this checkout the Petstore Swagger client example.

Caveats

Decorator order

Decorators can be basically added in any order, except for the HTTP method decorator (e.g. @GET()), which should always be at the top of the given decorator list. Third party decorators should be added above the HTTP method decorators.

Name conflicts

Decorators can sometimes generate conflicts with decorated method or function names in case they have the same name as they get merged into the __globals__ dictionary. In case this is an issue, decorest decorators should be used with full module namespace:

@decorest.POST('pet')
@decorest.content('application/json')
@decorest.header('accept', 'application/json')
@decorest.body('pet', lambda p: json.dumps(p))
def add_pet(self, pet):
    """Add a new pet to the store"""

Compatibility with other decorators

In general the decorators should work with other decorators, which return function objects, but your mileage may vary. In general third-party decorators should be added above the HTTP method decorators as only the HTTP decorators make the actual HTTP request. Thus, typical decorators, which try to wrap the actual call should get the HTTP callable returned by HTTP method decorators such as @GET().

Currently, it is not possible to add decorators such as @classmethod or @staticmethod to API methods, as the invocation requires an instance of client class.

Development

Create virtual env

# For Python 3
virtualenv -p /usr/bin/python3.8 venv3
source venv3/bin/activate

# For Python 2
virtualenv -p /usr/bin/python2.7 venv2
source venv2/bin/activate

Formatting

yapf -ir decorest tests examples

Running tests

All tests are stored in tests directory. Running tests is fully automated using tox and tox-docker.

# Python 3
python -m tox -e flake8,basic,httpbin,swaggerpetstore

# Python 2
python -m tox -c tox-py2.ini -e flake8,basic,httpbin,swaggerpetstore

Checking README syntax

rstcheck README.rst

License

Copyright 2018-present Bartosz Kryza <bkryza@gmail.com>

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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