prance 0.12.1

Command Line Interface

After installing prance, a CLI is available for validating (and resolving external references in) specs:

# Validates with resolving
$ prance validate path/to/swagger.yml

# Validates without resolving
$ prance validate --no-resolve path/to/swagger.yml

# Fetch URL, validate and resolve.
$ prance validate http://petstore.swagger.io/v2/swagger.json
Processing "http://petstore.swagger.io/v2/swagger.json"...
 -> Resolving external references.
Validates OK as Swagger/OpenAPI 2.0!

Validation is not the only feature of prance. One of the side effects of resolving is that from a spec with references, one can create a fully resolved output spec. In the past, this was done via options to the validate command, but now there’s a specific command just for this purpose:

# Compile spec
$ prance compile path/to/input.yml path/to/output.yml

Lastly, with the arrival of OpenAPI 3.0.0, it becomes useful for tooling to convert older specs to the new standard. Instead of re-inventing the wheel, prance just provides a CLI command for passing specs to the web API of swagger2openapi - a working internet connection is therefore required for this command:

# Convert spec
$ prance compile path/to/swagger.yml path/to/openapi.yml

Code

Most likely you have spec file and want to parse it:

from prance import ResolvingParser
parser = ResolvingParser('path/to/my/swagger.yaml')
parser.specification  # contains fully resolved specs as a dict

Prance also includes a non-resolving parser that does not follow JSON references, in case you prefer that.

from prance import BaseParser
parser = BaseParser('path/to/my/swagger.yaml')
parser.specification  # contains specs as a dict still containing JSON references

On Windows, the code reacts correctly if you pass posix-like paths (/c:/swagger) or if the path is relative. If you pass absolute windows path (like c:\swagger.yaml), you can use prance.util.fs.abspath to convert them.

URLs can also be parsed:

parser = ResolvingParser('http://petstore.swagger.io/v2/swagger.json')

Largely, that’s it. There is a whole slew of utility code that you may or may not find useful, too. Look at the full documentation for details.

Compatibility

Different validation backends support different features.

You can select the backend in the constructor of the parser(s):

parser = ResolvingParser('http://petstore.swagger.io/v2/swagger.json', backend = 'openapi-spec-validator')

Only the default backend is included in the dependencies; others are detected at run-time. If you install them, they can be used:

$ pip install openapi-spec-validator
$ pip install prance
$ prance validate --backend=openapi-spec-validator path/to/spec.yml

A note on strict mode: The OpenAPI specs are a little ambiguous. On the one hand, they use JSON references and JSON schema a fair bit. But on the other hand, what they specify as examples does not always match the JSON specs.

Most notably, JSON only accepts string keys in objects. However, some keys in the specs tend to be integer values, most notably the status codes for responses. Strict mode rejects non-string keys; the default lenient mode accepts them.

Since the flex validator is not based on JSON, it does not have this issue. The strict option therefore does not apply here.

Extensions

Prance includes the ability to reference outside swagger definitions in outside Python packages. Such a package must already be importable (i.e. installed), and be accessible via the ResourceManager API (some more info here).

For example, you might create a package common_swag with the file base.yaml containing the definition

definitions:
  Severity:
    type: string
    enum:
    - INFO
    - WARN
    - ERROR
    - FATAL

In the setup.py for common_swag you would add lines such as

packages=find_packages('src'),
package_dir={'': 'src'},
package_data={
    '': '*.yaml'
}

Then, having installed common_swag into some application, you could now write

definitions:
  Message:
    type: object
    properties:
      severity:
        $ref: 'python://common_swag/base.yaml#/definitions/Severity'
      code:
        type: string
      summary:
        type: string
      description:
        type: string
    required:
    - severity
    - summary