Running A Loop Until You See A Particular Result

[ibreeden]

but the problem is that when it does find a working proxy (response = 200), it still continues to check every other proxy anyway

Then add a break statement to exit the while loop after a successful connection.
And by the way, why do you want a random proxy? It might happen a false proxy is tried more than one time. It seems better to try the proxies in sequence. You may even try to change the order so the unsuccessful proxies are moved to the end.