def populate_backends(self, backends, context):
for name, uri in backends.items():<EOL><INDENT>self._backends_registry[name] = self._load_backend(uri, context)<EOL><DEDENT>
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.