Add support for extra_format_unmarshallers

[claeyswo]

There is already support for extra_format_validators and extra_media_type_deserializers:

pyramid_openapi3/pyramid_openapi3/__init__.py

Line 329 in ef0df8d

return {

Is it possible to add similar support for extra_format_unmarshallers?

https://github.com/python-openapi/openapi-core/blob/32ce65739531eea90220aeabbee72096818b9d05/openapi_core/unmarshalling/request/unmarshallers.py#L121

For now we are doing it like this:

   config.registry.settings["pyramid_openapi3"][
        "request_validator"
    ].extra_format_unmarshallers = {"search_filter": unmarshal_search_filter}
    config.registry.settings["pyramid_openapi3"][
        "response_validator"
    ].extra_format_unmarshallers = {"search_filter": unmarshal_search_filter}

[zupo]

This makes sense. Can you prepare a Pull Request with the required changes?

[claeyswo]

Sure, while implementing the change I discovered what I believe is a bug in openapi-core so I'm waiting for a fix for that.
python-openapi/openapi-core#821

[claeyswo]

PR is ready: #235