Dealing with scope in a recursive Python function-CodePudding

I have a JSON input file that looks like this:

{"nodes": [
    {"properties": {
        "id": "rootNode",
        "name": "Bertina Dunmore"},
      "nodes": [
        {"properties": {
            "id": 1,
            "name": "Gwenneth Rylett",
            "parent_id": "rootNode"},
          "nodes": [
            {"properties": {
                "id": 11,
                "name": "Joell Waye",
                "parent_id": 1}},
            {"properties": {
                "id": 12,
                "name": "Stan Willcox",
                "parent_id": 1}}]},
        {"properties": {
            "id": 2,
            "name": "Delbert Dukesbury",
            "parent_id": "rootNode"},
          "nodes": [
            {"properties": {
                "id": 21,
                "name": "Cecil McKeever",
                "parent_id": 2}},
            {"properties": {
                "id": 22,
                "name": "Joy Obee",
                "parent_id": 2}}]}]}]}

I want to get the nested properties dictionaries into a (flat) list of dictionaries. Creating a recursive function that will read this dictionaries is easy:

def get_node(nodes):
    for node in nodes:
        print(node['properties'])
        if 'nodes' in node.keys():
            get_node(node['nodes'])

Now, I'm struggling to append these to a single list:

def get_node(nodes):
    prop_list = []
    for node in nodes:
        print(node['properties'])
        prop_list.append(node['properties'])
        if 'nodes' in node.keys():
            get_node(node['nodes'])
    return prop_list

This returns [{'id': 'rootNode', 'name': 'Bertina Dunmore'}], even though all properties dictionaries are printed. I suspect that this is because I'm not handling the function scope properly.

Can someone please help me get my head around this?

CodePudding user response：

You need to combine the prop_list returned by the recursive call with the prop_list in the current scope. For example,

def get_node(nodes):
    prop_list = []
    for node in nodes:
        print(node['properties'])
        prop_list.append(node['properties'])
        if 'nodes' in node.keys():
            prop_list.extend(get_node(node['nodes']))
    return prop_list

CodePudding user response：

your problem is that every time you call get_node, the list where you append is initialized again. you can avoid this by passing the list to append in the recursive function

Moreover, I think would be nice to use dataclass to deal with this problem,

from dataclasses import dataclass

@dataclass
class Property:
    id: int
    name: str
    parent_id: str = None
    
        
def explore_json(data, properties: list=None):
    if properties is None:
        properties = []
    for key, val in data.items():
        if key == "nodes":
            for node in val:
                explore_json(node, properties)
        elif key == "properties":
            properties.append(Property(**val))
    return properties

explore_json(data)

output

[Property(id='rootNode', name='Bertina Dunmore', parent_id=None),
 Property(id=1, name='Gwenneth Rylett', parent_id='rootNode'),
 Property(id=11, name='Joell Waye', parent_id=1),
 Property(id=12, name='Stan Willcox', parent_id=1),
 Property(id=2, name='Delbert Dukesbury', parent_id='rootNode'),
 Property(id=21, name='Cecil McKeever', parent_id=2),
 Property(id=22, name='Joy Obee', parent_id=2)]

CodePudding user response：

With that:

def get_node(prop_list, nodes):
    for node in nodes:
        print(node['properties'])
        prop_list.append(node['properties'])
        if 'nodes' in node.keys():
            get_node(prop_list, node['nodes'])

You can just do:

prop_list = []
get_node(prop_list, <yourdictnodes>)

Should alter prop_list into:

{'id': 'rootNode', 'name': 'Bertina Dunmore'}
{'id': 1, 'name': 'Gwenneth Rylett', 'parent_id': 'rootNode'}
{'id': 11, 'name': 'Joell Waye', 'parent_id': 1}
{'id': 12, 'name': 'Stan Willcox', 'parent_id': 1}
{'id': 2, 'name': 'Delbert Dukesbury', 'parent_id': 'rootNode'}
{'id': 21, 'name': 'Cecil McKeever', 'parent_id': 2}
{'id': 22, 'name': 'Joy Obee', 'parent_id': 2}