title: Python : Writing to csv with headers
body: <p>I want to write a csv file with header in python and then append data to it by each run.But after each run the header as well as export_data is appended to the file. How can I prevent header to write each time?</p>
  
  <pre><code>ColA  ColB
  item1 item2
  item3 item4
  </code></pre>
  
  <p>Here is my code in python:</p>
  
  <pre><code>list1 = ['item1','item3']
  list2 = ['item2','item4']
  d = [list1,list2]
  export_data = it.zip_longest(*d, fillvalue = '')
  with open('D:/csv/csvfile.csv', 'a', newline='') as myfile:
      wr = csv.writer(myfile)
      wr.writerow(("colA", "colB",))
      wr.writerows(export_data)
  </code></pre>