find_free_dect_number.py

import json, requests
url = 'https://eventphone.de/guru2/phonebook?event=34C3&s=&page=1&format=json'

resp = requests.get(url=url, params=None)
output = json.loads(resp.text)

free_numbers = list(range(2100, 9999))

for entry in output:
	try:
		num = int(entry['extension'])
		free_numbers.remove(num)
	except Exception as e:
		continue

print('##############################################################################################')
print("##  ______                          _   _                       _                           ##")
print("## |  ____|                        | \ | |                     | |                          ##")
print("## | |__     _ __    ___    ___    |  \| |  _   _   _ __ ___   | |__     ___   _ __   ___   ##")
print("## |  __|   | '__|  / _ \  / _ \   | . ` | | | | | | '_ ` _ \  | '_ \   / _ \ | '__| / __|  ##")
print("## | |      | |    |  __/ |  __/   | |\  | | |_| | | | | | | | | |_) | |  __/ | |    \__ \\  ##")
print("## |_|      |_|     \___|  \___|   |_| \_|  \__,_| |_| |_| |_| |_.__/   \___| |_|    |___/  ##")
print("##                                                                                          ##")
print('##############################################################################################')
print("")
print(free_numbers)