Closing WSGI Middleware

# See http://blog.dscpl.com.au/2012/10/obligations-for-calling-close-on.html
class ClosingMiddleware(object):
    def __init__(self, application):
        self.application = application
        self.iterable = None

    def __call__(self, environ, start_response):
        self.iterable = self.application(environ, start_response)
        return self

    def __iter__(self):
        for data in self.iterable:
            yield data

    def close(self):
        if hasattr(self.iterable, 'close'):
            self.iterable.close()