title: Openpyxl.utils.exceptions.IllegalcharacterError
body: <p>I have the following python code to write processed words into excel file. The words are about 7729</p>
  <pre><code>From openpyxl import *
  book=Workbook ()
  sheet=book.active
  sheet.title=&quot;test&quot;
  for x in range (7729):
      sheet.cell (row=1,column=x+1).value=x
  book.save ('test.xlsx')
  </code></pre>
  <p>This is the what the code I used looks like, but when I run it, it gives me an error that says</p>
  <pre><code>openpyxl.utils.exceptions.IllegalCharacterError
  </code></pre>
  <p>This is my first time using this module, I would appreciate any kind of help.</p>