class BaseDatabaseClient:
    """Encapsulate backend-specific methods for opening a client shell."""
    # This should be a string representing the name of the executable
    # (e.g., "psql"). Subclasses must override this.
    executable_name = None

    def __init__(self, connection):
        # connection is an instance of BaseDatabaseWrapper.
        self.connection = connection

    def runshell(self):
        raise NotImplementedError('subclasses of BaseDatabaseClient must provide a runshell() method')