Swagger-Codegen (https://github.com/swagger-api/swagger-codegen) is a pretty mature, free and open-source project for generating API clients (e.g. ObjC, Java, C#, Ruby, Python, etc) and server stubs (e.g. PHP Slim, Java Spring, etc). Please give it a try and let us know your feedback by opening a ticket via https://github.com/swagger-api/swagger-codegen/issues
Disclosure: I'm a top contributor to the project.