title: Reference multiple cells with openpyxl
body: <p>I'm trying to reference multiple cells in a function using openpyxl, like is shown in this code:</p>
  
  <pre><code>from openpyxl.workbook import Workbook
  import os
  
  wb = Workbook()
  ws = wb.get_active_sheet()
  
  ws.cell("A1").value = 1
  ws.cell("A2").value = 2
  ws.cell("A3").value = "=SUM(A1;A2)"
  
  wb.save(os.path.join(os.getcwd(), "test.xlsx"))
  </code></pre>
  
  <p>When opening the output file with OpenOffice, the formula for cell A3 changes to <code>=SUM(A1|A2)</code> and the cell displays an error.</p>
  
  <p>Why did the ";" character change and how can I solve this?</p>