Twitter API: How to get users ID, who favorite specific tweet?

Apparently, the only way to do this is to scrape Twitter's website:

import urllib2
from lxml.html import parse

#returns list(retweet users),list(favorite users) for a given screen_name and status_id
def get_twitter_user_rts_and_favs(screen_name, status_id):
    url = urllib2.urlopen('https://twitter.com/' + screen_name + '/status/' + status_id)
    root = parse(url).getroot()

    num_rts = 0
    num_favs = 0
    rt_users = []
    fav_users = []

    for ul in root.find_class('stats'):
        for li in ul.cssselect('li'):

            cls_name = li.attrib['class']

            if cls_name.find('retweet') >= 0:
                num_rts = int(li.cssselect('a')[0].attrib['data-tweet-stat-count'])

            elif cls_name.find('favorit') >= 0:
                num_favs = int(li.cssselect('a')[0].attrib['data-tweet-stat-count'])

            elif cls_name.find('avatar') >= 0 or cls_name.find('face-pile') >= 0:#else face-plant

                for users in li.cssselect('a'):
                    #apparently, favs are listed before retweets, but the retweet summary's listed before the fav summary
                    #if in doubt you can take the difference of returned uids here with retweet uids from the official api
                    if num_favs > 0:#num_rt > 0:
                        #num_rts -= 1
                        num_favs -= 1
                        #rt_users.append(users.attrib['data-user-id'])
                        fav_users.append(users.attrib['data-user-id'])
                    else:                        
                        #fav_users.append(users.attrib['data-user-id'])
                        rt_users.append(users.attrib['data-user-id'])

        return rt_users, fav_users


#example
if __name__ == '__main__':
    print get_twitter_user_rts_and_favs('alien_merchant', '674104400013578240')

Twitter API v2 has new likes functionality:

https://twittercommunity.com/t/announcing-twitter-api-v2-likes-lookup-and-blocks-lookup/154353

To get users who have liked a Tweet, use the GET /2/tweets/:id/liking_users endpoint.

They've also provided example code on their github repo.

Short answer: You can't do this perfectly.

Long answer: You can do this with some effort but it isn't going to be even close to perfect. You can use the twitter api to monitor the activity of up to 4000 user id's. If a tweet is created by one of the 4k people you monitor, then you can get all the information including the people who have favourited the tweet. This also requires that you push all the information about the people you monitor onto a database (I use mongodb). You can then query the database for information about your tweet.