'Returns the default source_translator setting for token representations.
Most links are token-based: given a target token index, retrieve a learned
representation for that token from this component. This depends on the
transition system; e.g. we should make sure that left-to-right sequence
models reverse the incoming token index when looking up representations from
a right-to-left model.
Returns:
String name of default translator for this transition system.
Raises:
ValueError: if no default is known for the given setup.'

def default_token_translator(self):

    transition_spec = self.spec.transition_system
    if (transition_spec.registered_name == 'arc-standard'):
        return 'shift-reduce-step'
    if (transition_spec.registered_name in ('shift-only', 'tagger')):
        if ('left_to_right' in transition_spec.parameters):
            if (transition_spec.parameters['left_to_right'] == 'false'):
                return 'reverse-token'
        return 'identity'
    raise ValueError(('Invalid    transition    spec:    %s' % str(transition_spec)))
