Python For循环中元素定位失效：为什么在 Excel 参数化测试中，循环执行后定位元素失败，而调整浏览器调用位置后就能解决问题？

import unittest
import time
import xlrd
from selenium import webdriver

def open_excel(file):
    try:
        data = xlrd.open_workbook(file)
        return data
    except Exception as e:
        print(str(e))

def excel_table_byindex(file, colnameindex=0, by_index=0):
    data = open_excel(file)
    table = data.sheets()[by_index]
    nrows = table.nrows
    colnames = table.row_values(colnameindex)
    list = []
    for rownum in range(1, nrows):
        row = table.row_values(rownum)
        if row:
            app = {}
            for i in range(len(colnames)):
                app[colnames[i]] = row[i]
            list.append(app)
    return list

class login(unittest.TestCase):

    def setUp(self):
        self.driver = webdriver.Firefox()
        self.driver.maximize_window()
        self.driver.implicitly_wait(10)
        self.driver.get("https://passport.meituan.com/account/unitivelogin?service=www&continue=http%3A%2F%2Fwww.meituan.com%2Faccount%2Fsettoken%3Fcontinue%3Dhttps%253A%252F%252Fwww.meituan.com%252F")
        time.sleep(5)

    def test(self):
        tabls = excel_table_byindex(file='./data/meit.xlsx')
        print(tabls)
        if (len(tabls) <= 0):
            assert 0, u"数据异常"
        for i in range(0, len(tabls)):
            print(i)
            print(tabls[i]['username'])
            print(tabls[i]['password'])
            # 登录
            self.driver.find_element_by_id('login-email').send_keys(tabls[i]['username'])
            self.driver.find_element_by_id("login-password").send_keys(tabls[i]['password'])
            self.driver.find_element_by_class_name('btn').click()
            time.sleep(3)

    def tearDown(self):
        time.sleep(3)
        self.driver.quit()

if __name__ == '__main__':
    unittest.main()