A small change

cfg = {
    'level_1': {
        'level_2': {
            'item1': 10,
            'item2': 20,
        }
    }
}


class Cache:
    def __init__(self, **data):
        self.nodes = data

    def get(self, uri=None):

        def walk(_uri, nodes):
            parts = _uri.split('/', 1)
            key = parts.pop(0)

            if key in nodes:
                node = nodes[key]

                if not parts:
                    return node
                else:
                    return walk(parts[0], node)

        return walk(uri, self.nodes)

    def set(self, uri, value=None):

        def walk(_uri, nodes):
            parts = _uri.split('/', 1)
            key = parts.pop(0)

            if key in nodes and parts:
                return walk(parts[0], nodes[key])
            elif len(_uri.split('/')) == 1:
                nodes[key] = value

        return walk(uri, self.nodes)


c = cache = Cache(**cfg)

print(c.get('level_1/level_2/item2'))
c.set('level_1/level_2/item3', 100)
print(c.get('level_1/level_2/item3'))