def getContainer(name_or_id):
    '''Get the container with the given name or ID (str). No side effects.
    Idempotent. Returns None if the container does not exist. Otherwise, the
    continer is returned'''
    require_str("name_or_id", name_or_id)

    container = None
    try:
        container = client.containers.get(name_or_id)
    except NotFound as exc:
        # Return None when the container is not found
        pass
    except APIError as exc:
        eprint("Unhandled error")
        raise exc

    return container