May be it's a stupid question, but how to get a Secret not created by pulumi when I know the name and the namespace. I guess something like this in python

machine_secret = kubernetes.core.v1.Secret.get(
            "pulumi_resource_name",
            "secret_name_in_k8s_cluster",
        )

but where to filter the namespace? It's not allowed input arg.

the secret name is in the form

namespace/name

This one gets a secret managed by Pulumi. To get one outside of pulumi, you have to use the regular Kubernetes client for your language.