This is a simple Python port of the Tor's code for generating hidden service descriptor id's. Haven't tested this snippet so there might be a syntax error or something

tor-desc-id-calc.py

#!/usr/bin/env python
from time import time
from base64 import b32encode, b32decode, b16decode
from hashlib import sha1
from struct import pack, unpack

# When provided with a Tor hidden service 'service_id', this script should output
# the desc_id's which clients would request at the current time .

# Based on rend_compute_v2_desc_id() from rendcommon.c in Tor source code.
def compute_desc_ids(service_id_base32, max_replicas, time = int(time()), descriptor_cookie = ""):
  desc_ids = []
  for replica in range(0, max_replicas):
    desc_ids.append(rend_compute_v2_desc_id(service_id_base32, replica, time, descriptor_cookie))
  return desc_ids

# Returns base_32 encode desc_id - descriptor-id = H(permanent-id | H(time-period | descriptor-cookie | replica))
def rend_compute_v2_desc_id(service_id_base32, replica, time, descriptor_cookie):#
   service_id = b32decode(service_id_base32, 1)
   time_period = get_time_period(time, 0, service_id)
   secret_id_part = get_secret_id_part_bytes(time_period, descriptor_cookie, replica)
   desc_id = rend_get_descriptor_id_bytes(service_id, secret_id_part)
   return b32encode(desc_id).lower()

# Calculates time period - time-period = (current-time + permanent-id-byte * 86400 / 256) / 86400
def get_time_period(time, deviation, service_id):
  REND_TIME_PERIOD_V2_DESC_VALIDITY = 24 * 60 * 60
  return int(((time + ((unpack('B', service_id[0])[0] * REND_TIME_PERIOD_V2_DESC_VALIDITY) ) / 256) ) / REND_TIME_PERIOD_V2_DESC_VALIDITY + deviation)

# Calculate secret_id_part - secret-id-part = H(time-period | descriptor-cookie | replica)
def get_secret_id_part_bytes(time_period, descriptor_cookie, replica):
  secret_id_part = sha1()
  secret_id_part.update(pack('>I', time_period)[:4]);
  if descriptor_cookie:
    secret_id_part.update(descriptor_cookie)
  secret_id_part.update('{0:02X}'.format(replica).decode('hex'))
  return secret_id_part.digest()

def rend_get_descriptor_id_bytes(service_id, secret_id_part):
  descriptor_id = sha1()
  descriptor_id.update(service_id)
  descriptor_id.update(secret_id_part)
  return descriptor_id.digest()

def main():
    REPLICAS = 2
    onion_address = "idnxcnkne4qt76tg.onion"
    
    service_id, tld = onion_address.split(".")
    if tld == 'onion' and len(service_id) == 16 and service_id.isalnum():
        desc_ids = compute_desc_ids(service_id, REPLICAS)
        
    print desc_ids
  
main()

The OR identity_digest is just the base32 encoding of the SHA1 hash of the OR public identity key. Same hash as the OR fingerprint, just base32 encoded rather than the base16 encoding of the fingerprint.