Cornice Web Services for Pyramid

6.1.0 · active · verified Fri Apr 17

Cornice is a Python library that simplifies the definition of RESTful web services within the Pyramid web framework. It allows developers to declare services, resources, and their methods using decorators and schema validation, often integrating with tools like Colander and Marshmallow. The current version is 6.1.0, and it maintains an active release cadence, frequently updating for Python and Pyramid compatibility and addressing dependencies.

Common errors

```
ImportError: cannot import name 'Service' from 'cornice'
```
cause Incorrect import path; 'Service' is directly available in the top-level 'cornice' package, not a submodule.

fix Change the import to `from cornice import Service`.
```
AttributeError: 'Service' object has no attribute 'add_get'
```
cause Attempting to use older, deprecated `add_` methods (e.g., `add_get`, `add_post`) instead of the decorator syntax for defining service methods.

fix Use the decorator syntax for defining service methods, e.g., `@service.get()` or `@service.post()`.
```
TypeError: 'Request' object is not subscriptable
```
cause Attempting to access request attributes like `request['json']` or `request['validated']` using dictionary-style bracket notation.

fix Access request data using dot notation: `request.json` or `request.validated`.
```
colander.Invalid: ... missing or invalid fields ...
```
cause Validation failed because the request body or parameters do not conform to the defined Colander schema. This often indicates missing required fields or incorrect data types.

fix Review your Colander schema definition and ensure the incoming request data (e.g., JSON body, query parameters) matches the expected structure and types. Check logs for specific field errors.

Warnings

breaking Cornice 6.0.0 dropped support for Marshmallow versions older than 3. Attempting to use an older Marshmallow version will lead to compatibility issues or errors.
Fix: Upgrade Marshmallow to version 3 or higher using `pip install 'marshmallow>=3.0.0'`.
breaking Cornice 5.0.0 dropped support for Python 2.x. Applications running on Python 2 will not be compatible with Cornice versions 5.0.0 and above.
Fix: Migrate your application codebase to Python 3.x to use Cornice 5.0.0 or newer.
gotcha In Cornice 5.0.2, the internal default JSON renderer name changed from `cornice` to `cornicejson`. While this change was not officially documented as a breaking change, applications explicitly relying on or configuring a renderer named 'cornice' might experience issues.
Fix: If you had `config.add_renderer('cornice', 'some.renderer.path')` or similar, update it to use `cornicejson` if you relied on the implicit name, or ensure your renderer configuration explicitly maps to the desired name.
gotcha Prior to Cornice 5.0.3, Colander validators (e.g., `body_validator`) might incorrectly miss `body`, `headers`, `path`, or `querystring` data from the request, leading to incomplete validation.
Fix: Upgrade to Cornice 5.0.3 or higher to ensure Colander validators receive all expected request data for accurate validation.

Install

pip install cornice Install stable version

Imports

Service
wrong:
```
from cornice.service import Service
```
correct:
```
from cornice import Service
```
Service is directly exposed at the top level of the cornice package.
resource
```
from cornice.resource import resource
```
Used to define resources with multiple services and CRUD operations.
validators
```
from cornice import validators
```
Access to built-in validators, often used with Colander schemas.

Quickstart

This quickstart demonstrates how to define a simple 'Hello World' service using Cornice within a standalone Pyramid application. Run this script, then access `http://0.0.0.0:6543/hello` in your browser or with `curl`.

from wsgiref.simple_server import make_server
from pyramid.config import Configurator

from cornice import Service

# 1. Define a Cornice service
hello_service = Service(name='hello', path='/hello', description="Hello World Service")

@hello_service.get()
def get_hello(request):
    """Returns a 'Hello World!' message."""
    # Access request data via request.GET, request.json, request.validated, etc.
    return {'message': 'Hello World! from Cornice!'}

# 2. Integrate into a Pyramid application
if __name__ == '__main__':
    with Configurator() as config:
        # Include the cornice package to register its components
        config.include('cornice')

        # Add the defined Cornice service to the Pyramid configuration
        config.add_cornice_service(hello_service)

        # Create a WSGI application
        app = config.make_wsgi_app()
    
    # 3. Run the Pyramid application
    server = make_server('0.0.0.0', 6543, app)
    print('Serving on http://0.0.0.0:6543/hello')
    print('Press Ctrl+C to quit')
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        pass
    finally:
        server.server_close()

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