catcher.py

import time

key = input('key> ')

with open('data.dat','r',encoding='utf-8') as data:
    for line in data:
        if line.rstrip() == '##%s-start' % key:
            line.replace('##%s-start' % key,'')
            break

    for line in data:
        if line.rstrip() == '%user_name%':
            print('ok')

    for line in data:
        if line.rstrip() == '##%s-end' % key:
            line.replace('##%s-end' % key,'')
            break

        for i in range(len(line)):
            print(line[i],end='')
            time.sleep(.05)