docs: def read_follower_file(fname, min_followers=0, max_followers=1e10, blacklist=set()):
      """ Read a file of follower information and return a dictionary mapping screen_name to a set of follower ids. """
      result = {}
      with open(fname, 'rt') as f:
          for line in f:
              parts = line.split()
              if len(parts) > 3:
                  if parts[1].lower() not in blacklist:
                      followers = set(int(x) for x in parts[2:])
                      if len(followers) > min_followers and len(followers) <= max_followers:
                          result[parts[1].lower()] = followers
                  else:
                      print('skipping exemplar', parts[1].lower())
      return result