title: Why can't I edit my .xlsx file with openpyxl?
body: <p>I am encountering a problem when running with openpyxl the code below</p>
  
  <pre><code>import openpyxl
  import os
  
  wb = openpyxl.load_workbook('example.xlsx')
  sheet = wb.get_sheet_by_name('Sheet1')
  sheet["A1"].value
  sheet["A1"].value == None
  sheet["A1"].value = 42
  sheet["A3"].value = 'Hello'
  os.chdir("/Users/mac/Desktop")
  wb.save('exceeeel.xlsx')
  </code></pre>
  
  <p>The error is</p>
  
  <pre><code> File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/openpyxl/reader/excel.py", line 312, in load_wo
  rkbook
      reader = ExcelReader(filename, read_only, keep_vba,
    File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/openpyxl/reader/excel.py", line 124, in __init_
  _
      self.archive = _validate_archive(fn)
    File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/openpyxl/reader/excel.py", line 96, in _validat
  e_archive
  </code></pre>
  
  <p>What am I doing wrong? I am using the current version of the openpyxl library.</p>