title: Openpyxl xlsx results are appending instead of overwriting
body: <p>I'm using openpyxl to write results to an excel file.  The problem is when I run the script a second time, the results appear underneath the first results instead of overwriting them as I would like.  So, currently the first results appear in rows 2-151 and the 2nd results are appended in rows 152-301. I would like the second results to overwrite the first results in rows 2-151.  </p>
  
  <p>Anyone know if this possible to fix?</p>
  
  <p>Thanks</p>
  
  <pre><code>from time import sleep
  from selenium import webdriver
  from selenium.webdriver.common.by import By
  from selenium.webdriver.support.ui import WebDriverWait
  from selenium.webdriver.support import expected_conditions as EC
  from selenium.common.exceptions import TimeoutException
  import openpyxl
  from openpyxl import load_workbook
  
  url = 'http://www.tradingview.com/screener'
  driver = webdriver.Firefox()
  driver.get(url)
  
  # will give a list of all tickers
  tickers = driver.find_elements_by_css_selector('a.tv-screener__symbol')
  
  wb = load_workbook('C:/Users/Jake/results.xlsx')
  sheet = wb["Sheet2"]
  
  for index in range(len(tickers)):
     row = [tickers[index].text]
     sheet.append(row)
  
  wb.save('C:/Users/Jake/results.xlsx')
  </code></pre>