def populate_backends(self, backends, context):
        """
        Iterate over the given backends list and instantiate every backend
        found. Can raise :exc:`BackendNotFoundError` if a backend
        could not be found in the registered entry points.

        The `backends` parameter should be a dict with backend names as keys
        and URIs as values.
        """
        for name, uri in backends.items():
            self._backends_registry[name] = self._load_backend(uri, context)