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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_node_groups(self):
 """Return a list of node id lists that are topologically identical. First construct a node_dict which is keyed to the node id and has a value which is a dict with keys 'sources' and 'targets'. The 'sources' and 'targets' each contain a list of tuples (i, polarity, source) edge of the node. node_dict is then processed by _get_node_key() which returns a tuple of (s,t) where s,t are sorted tuples of the ids for the source and target nodes. (s,t) is then used as a key in node_key_dict where the values are the node ids. node_groups is restricted to groups greater than 1 node. """

        node_dict = {node['data']['id']: {'sources': [], 'targets': []}
                     for node in self._nodes}
        for edge in self._edges:
            # Add edge as a source for its target node
            edge_data = (edge['data']['i'], edge['data']['polarity'],
                         edge['data']['source'])
            node_dict[edge['data']['target']]['sources'].append(edge_data)
            # Add edge as target for its source node
            edge_data = (edge['data']['i'], edge['data']['polarity'],
                         edge['data']['target'])
            node_dict[edge['data']['source']]['targets'].append(edge_data)
        # Make a dictionary of nodes based on source/target as a key
        node_key_dict = collections.defaultdict(lambda: [])
        for node_id, node_d in node_dict.items():
            key = self._get_node_key(node_d)
            node_key_dict[key].append(node_id)
        # Constrain the groups to ones that have more than 1 member
        node_groups = [g for g in node_key_dict.values() if (len(g) > 1)]
        return node_groups