title: TypeError: to_append should be a Series or list/tuple of Series, got DataFrame
body: <p>Code was working earlier then just stopped.</p>
  <p>I don't understand why, if somebody could help me with shedding some light on the subject that would be awesome.</p>
  <pre><code>import urllib.request
  from bs4 import BeautifulSoup as bs
  import re
  import pandas as pd
  import requests
  
  
  locations = ['las-vegas-nv','denver-co']
  for location in locations:
      headers = {
          'User-Agent' : 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.93 Safari/537.36'
      }
  
  
  
      url = f'https://www.apartments.com/{location}/1-bedrooms/'
      page = requests.get(url, headers=headers)
      soup = bs(page.text, 'lxml')
      table = soup.find(&quot;table&quot;, class_=&quot;rentTrendGrid&quot;)
      rows = []
  
      for tr in table.find_all('tr'):
          rows.append([td.text for td in tr.find_all(['th', 'td'])])
  
  #header_row = rows[0]
      rows = list(zip(*rows[0:])) # tranpose the table
      df = pd.DataFrame(rows[1:], columns=rows[0])
      df['City'] = location
      dfs.append(df)
      df = pd.concat(dfs).reset_index(drop = True)
  print(df)
  </code></pre>