Best Of

@Alessio_Pagliano I actually recently went through this process recently and wrote a python script that handles steps 3 and 4 in my prior comment. Hope it helps!

import logging
import csv
import requests

# Logging config
logging.basicConfig(level=logging.INFO)
_logger = logging.getLogger(__name__)

workspaceId = "8a88807f9a"
modelId = "0FED08BFA32D"

outputFilename="subset_details.csv"

 ## This script assumes you already have an auth token returned from a prior authentication call. If not, you will need to add extra code to authenticate.
anaplan_token = "bahbas6512sdfvs"
request_headers = {
    "Authorization": "AnaplanAuthToken {}".format(anaplan_token),
    "Accept": "application/json"
}

 ## This script assumes you have already generated a list of listIds of all the subsets. If not, you will need to add extra code to generate this list.
listsWithSubsets = [101000000019,101000000016]

subsets = [] # Initialize the subsets array to be populated by the below code
for l in listsWithSubsets:
    _logger.info(f"Sending metadata request for list {l}.")
    r_getListDetails = f"https://api.anaplan.com/2/0/workspaces/{workspaceId}/models/{modelId}/lists/{l}"
    r = requests.get(url=r_getListDetails, headers=request_headers)
    data = r.json()

    _logger.debug(f"Response with metadata:\n{data['metadata']}")
    listId = data['metadata']['id']
    listName = data['metadata']['name']
    subsetList = data['metadata']['subsets']

    _logger.info(f"{len(subsetList)} subsets found for list {l}. Getting subset details.")
    for s in subsetList:
        subset = {}
        subset['listId'] = listId
        subset['listName'] = listName
        subset['id'] = s['id']
        subset['name'] = s['name']
        r_getListItems = f"https://api.anaplan.com/2/0/workspaces/{workspaceId}/models/{modelId}/dimensions/{subset['id']}/items"
        r = requests.get(url=r_getListItems, headers=request_headers)
        data = r.json()
        subset['count'] = 0
        if "items" in data:
            subset['count'] = len(data['items'])
        _logger.info(f"{subset['count']} items found. Appending to list.")
        subsets.append(subset)

_logger.info(f"Contents of the 'subsets' array: {subsets}")

_logger.info(f"Generating csv file '{outputFilename}'")
with open(outputFilename, 'w', newline='') as f:
    writer = csv.writer(f, quoting=csv.QUOTE_ALL)
    writer.writerow(['List Id','List Name','Subset Id','Subset Name','Item Count'])
    for s in subsets:
        writer.writerow([s['listId'],s['listName'],s['id'],s['name'],s['count']])