Python Selenium遇NoSuchElementException：元素存在却无法定位

我在开发网页爬虫时，尝试定位页面中的select元素，Selenium始终找不到目标对象，直接抛出NoSuchElementException异常。我已经确认XPATH是正确的，用它调用find_element方法还是无效；也试过通过name属性定位，但目前场景下XPATH应该是唯一可行的方式。问题出在代码最后一行的select元素定位逻辑，以下是完整代码：

import data
import time
from selenium import webdriver
from selenium.webdriver.support.ui import Select
from selenium.webdriver.common.by import By

driver = webdriver.Chrome()
driver.get(data.login_site)

username_input = driver.find_element(By.NAME, "_username")
username_input.send_keys(username)
password_input = driver.find_element(By.NAME, "_password")
password_input.send_keys(password)

login_button = driver.find_element(By.XPATH, "//button[@class='btn btn-primary']")
login_button.click()

plaene_button = driver.find_element(By.XPATH, "//a[@href='/iserv/plan/overview']")
plaene_button.click()

plaene_show = driver.find_element(By.XPATH, "//a[@href='/iserv/plan/show/Plan%20Schueler']")
plaene_show.click()

time.sleep(4)
drpdClass = Select(driver.find_element(By.XPATH, "/html/body/table/tbody/tr/td/form/table/tbody/tr/td[3]/span/nobr/select"))

time.sleep(10)

网站截图：

内容的提问来源于stack exchange，提问作者Elias Petrat