AttributeError: 'str' object has no attribute 'descendants'

from bs4 import BeautifulSoup as bs
import webbrowser
import requests
from lxml import html
from selenium import webdriver
profile = webdriver.FirefoxProfile()
profile.accept_untrusted_certs = True
import time

# selenium
wd = webdriver.Firefox(executable_path="C:/Utility/geckodriver.exe", firefox_profile=profile)
url = "https://airflow.cruxinternal.com/admin/?page=0"
wd.get(url)

# set username
time.sleep(2)
username = wd.find_element_by_id("identifierId")
username.send_keys("my_email@email.com")
wd.find_element_by_id("identifierNext").click()

# set password
time.sleep(2)
password = wd.find_element_by_name("password")
password.send_keys("my_pswd")
wd.find_element_by_id("passwordNext").click()

all_text = []

# list of URLs
url_list = ['https://airflow.cruxinternal.com/admin/airflow/graph?dag_id=barra_emm1_daily_legacy',
'https://airflow.cruxinternal.com/admin/airflow/graph?dag_id=barra_emm1_daily_legacy_history']
for link in url_list:
    #File = webbrowser.open(link)
    #File = requests.get(link)
    #data = File.text
    for link in bs.findAll('tspan'):
        alldata = all_text.append(link.get('tspan'))

outF = open('C:/Users/ryans/OneDrive/Desktop/test.txt', 'w')
outF.writelines(alldata)
outF.close()