It was written in pure python3 and using the low-level networking interface in Python's core.
Intended to be used with 1 argument (e.g. 8.8.8.8 or 10.10.0.0/16 as examples.)
If parallelism is extremely necessary, GNU parallel is highly recommended.
It's way faster than Nmap. Below is a very simple test using a high-speed network with very low latency to some known DNS servers around the globe.
└─$ time sudo nmap -T5 -n -P0 -sU -p53 --open --script=dns-recursion 1.1.1.3 && time ./scan-dns-openresolvers.py 1.1.1.3
Starting Nmap 7.94 ( https://nmap.org ) at 2023-06-20 17:54 UTC
Nmap scan report for 1.1.1.3
Host is up (0.0033s latency).
PORT STATE SERVICE
53/udp open domain
|_dns-recursion: Recursion appears to be enabled
Nmap done: 1 IP address (1 host up) scanned in 0.23 seconds
real 0m0.266s
user 0m0.000s
sys 0m0.010s
1.1.1.3,open,1687283676
real 0m0.035s
user 0m0.030s
sys 0m0.000s