from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
delay = 5

username = driver.find_element_by_name('Username')
password = driver.find_element_by_name('Password')
username.send_keys('my_username')
password.send_keys('my_password')
login = driver.find_element_by_id('login_button')
login.click()

button_a = driver.find_element_by_id('button_a')
button_a.click()
WebDriverWait(driver, delay).until(
    EC.presence_of_element_located(
        driver.find_element_by_id('button_b')))

selenium.common.exceptions.NoSuchElementException: Message: no such element:     Unable to locate element: {"method":"id","selector":"button_b"}