yields nodes from graph are the specified source.

def get_nodes_by_source(self, graph, source_full_name):
        """yields nodes from graph are the specified source."""
        parts = source_full_name.split('.')
        if len(parts) == 1:
            target_source, target_table = parts[0], None
        elif len(parts) == 2:
            target_source, target_table = parts
        else:  # len(parts) > 2 or len(parts) == 0
            msg = (
                'Invalid source selector value "{}". Sources must be of the '
                'form `${{source_name}}` or '
                '`${{source_name}}.${{target_name}}`'
            ).format(source_full_name)
            raise dbt.exceptions.RuntimeException(msg)

        for node, real_node in self.source_nodes(graph):
            if target_source not in (real_node.source_name, SELECTOR_GLOB):
                continue
            if target_table in (None, real_node.name, SELECTOR_GLOB):
                yield node