In CircuitPython

twitter_followers.py

import json
import urequests
import base64

with open("config.json") as fp:
    config = json.load(fp)

if config['key'] is None:
    raise KeyError("No twitter API key")
if config['secret'] is None:
    raise KeyError("No twitter API secret")

# you should be url encoding the keys but we can't in CP
key = base64.b64encode(config['key'] + ':' + config['secret'])

url = "https://api.twitter.com/oauth2/token"
header = {
        "Authorization": "Basic " + key,
        "Content-Type": "application/x-www-form-urlencoded;charset=UTF-8"
        }
body = {
        "grant_type": "client_credentials"
        }

r = urequests.post(url, data=body, headers=header)
decoded = r.json()
token = decoded['access_token']

username = "sigafoos"
url = "https://api.twitter.com/1.1/followers/ids.json?cursor=-1&screen_name=%s&count=5000" % username
header = {
        "Authorization": "Bearer " + token
        }
r = urequests.get(url, headers=header)
decoded = r.json()

num_followers = len(decoded['ids'])