Nested dictionary creation with setdefault

Question

Is there a better way of creating a nested dictionary than what I'm doing below? The result for the setdefault is because I don't know whether that particular key exists yet or not.

def record_execution_log_action(
 execution_log, region, service, resource, resource_id, resource_action
 ):
 execution_log["AWS"].setdefault(region, {}).setdefault(service, {}).setdefault(
 resource, []
 ).append(
 {
 "id": resource_id,
 "action": resource_action,
 "timestamp": datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S"),
 }
 )

• theProgrammer: You can used a defaultdict from collections module instead, it automatically creates the default( this can be a list) if the key is not found.
• mlevit: I've created about defaultdict but I don't get how to use it for my nested use case properly. Could you give an example?

Answer 1

Use a defaultdict like so:

from collections import defaultdict
resource_dict = lambda: defaultdict(list)
service_dict = lambda: defaultdict(resource_dict)
region_dict = lambda: defaultdict(service_dict)
execution_log = defaultdict(region_dict)
execution_log['AWS']['region']['service']['resource'].append({
 "id": 'resource_id',
 "action": 'resource_action',
 "timestamp": "%Y-%m-%d %H:%M:%S",
 })
execution_log

output:

defaultdict(<function __main__.<lambda>()>,
 {'AWS': defaultdict(<function __main__.<lambda>()>,
 {'region': defaultdict(<function __main__.<lambda>()>,
 {'service': defaultdict(list,
 {'resource': [{'id': 'resource_id',
 'action': 'resource_action',
 'timestamp': '%Y-%m-%d %H:%M:%S'}]})})})})