Request Handling

Connexion validates incoming requests for conformance with the schemas described in swagger specification.

Request parameters will be provided to the handler functions as keyword arguments if they are included in the function’s signature, otherwise body parameters can be accessed from connexion.request.json and query parameters can be accessed from connexion.request.args.

Request Validation

Both the request body and parameters are validated against the specification, using jsonschema.

If the request doesn’t match the specification connexion will return a 400 error.

Automatic Parameter Handling

Connexion automatically maps the parameters defined in your endpoint specification to arguments of your Python views as named parameters and with value casting whenever possible. All you need to do is define the endpoint’s parameters with matching names with your views arguments.

As example you have a endpoint specified as:

      operationId: api.foo_get
        - name: message
          description: Some message.
          in: query
          type: string
          required: true

And the view function:

# file

def foo_get(message):
    # do something
    return 'You send the message: {}'.format(message), 200

In this example Connexion will automatically identify that your view function expects an argument named message and will assign the value of the endpoint parameter message to your view function.

Connexion will also use default values if they are provided.


Please note that when you have a parameter defined as not required at your endpoint and your Python view have a non-named argument, when you call this endpoint WITHOUT the parameter you will get an exception of missing positional argument.

Type casting

Whenever possible Connexion will try to parse your argument values and do type casting to related Python natives values. The current available type castings are:

Swagger Type Python Type
integer int
string str
number float
boolean bool
array list
object dict

In the Swagger definition if the array type is used you can define the collectionFormat that it should be recognized. Connexion currently supports collection formats “pipes” and “csv”. The default format is “csv”.

Nullable parameters

Sometimes your API should explicitly accept nullable parameters. However OpenAPI specification currently does not support officially a way to serve this use case, Connexion adds the x-nullable vendor extension to parameter definitions. It’s usage would be:

     - name: name
       in: query
       type: string
       x-nullable: true
       required: true

It is supported by Connexion in all parameter types: body, query, formData, and path. Nullable values are the strings null and None.


Be careful on nullable paramenters for sensitive data where the strings “null” or “None” can be valid values.


This extension will be removed as soon as OpenAPI/Swagger Specification provide a official way of supporting nullable values.

Header Parameters

Currently header parameters are not passed to the handler functions as parameters. But they can be accessed through the underlying connexion.request.headers object which aliases the flask.request.headers object.

def index():
    page_number = connexion.request.headers['Page-Number']