POST from python and nested loop

taxiCalculator.py

import requests, json
open('output.txt', 'w').close()
with open('towns.txt') as f:
    lines = f.readlines()
    length = len(lines)
    i = 0
    while i < length:
        for j in range(i, length):
            begin = lines[i].strip('\n')
            end = lines[j].strip('\n')
            headers = {'content-type': 'application/x-www-form-urlencoded'}
            payload = {'from': begin, 'to': end, 'class': 1}
            r = requests.post("http://taxi-avrora-krim.ru/php/upload-price.php", data=payload, headers=headers, verify=False)
            #print(lines[i].rstrip('\n'), end=',')
            #print(lines[j].rstrip('\n'), end=',')
            #data = json.loads(r.text)
            #print(data['price'])
            with open('output.txt', 'a') as of:
                data = json.loads(r.text)
                t_output = lines[i].rstrip('\n')
                n_output = lines[j].rstrip('\n')
                p_output = data['price']
                print(f"{t_output}, {n_output}, {p_output}", file=of)

        i += 1