count_tweets.py

#!/usr/bin/env python
import tweepy
from collections import Counter

consumer_key = 'consumer_key'
consumer_secret = 'consumer_secret'
access_token = 'access_token'
access_token_secret = 'access_token_secret'

auth = tweepy.OAuthHandler(consumer_key, consumer_secret)
auth.set_access_token(access_token, access_token_secret)

api = tweepy.API(auth)

def process(tweet):
  return tweet.author.screen_name

results = []
for tweet in tweepy.Cursor(api.search, q='HASHTAG').items():
  results.append(process(tweet))

counts = Counter(results)
print(counts)