Initialise the formatter with app-specific values from ``app``’s configuration

def init_app(self, app):
        """Initialise the formatter with app-specific values from ``app``’s configuration
        """

        if self.__inited:
            return

        config = app.config.get(
            'FLASK_LOGGING_EXTRAS', {})

        blueprint_config = config.get('BLUEPRINT', {})
        self.bp_var = blueprint_config.get('FORMAT_NAME', 'blueprint')
        self.bp_app = blueprint_config.get('APP_BLUEPRINT', '<app>')
        self.bp_noreq = blueprint_config.get('NO_REQUEST_BLUEPRINT', '<not a request>')

        for var_name, resolver_fqn in config.get('RESOLVERS', {}).items():
            if resolver_fqn is None:
                resolver = None
            else:
                try:
                    resolver = _import_by_string(resolver_fqn)
                except ImportError:
                    resolver = resolver_fqn

            self.resolvers[var_name] = resolver

            self.__inited = True