title: Modify an existing xlsx file with python
body: <p>I have an issue with the use of Pandas + ExcelWriter + load_workbook.
  My need is to be able to modify data from an existing excel file (without deleting the rest).
  It works partly, but when I check the size of the produced file and the original one the size is quite different.
  Moreover, it seems to lack some properties. Which leads to an error message when I want to integrate the modified file into an application.
  The code bellow :</p>
  <pre><code>data_filtered = pd.DataFrame([date, date, date, date], index=[2,3,4,5])
  book = openpyxl.load_workbook(file_origin)
  writer = pd.ExcelWriter(file_modif, engine='openpyxl',datetime_format='dd/mm/yyyy hh:mm:ss', date_format='dd/mm/yyyy')
  writer.book = book
  ## ExcelWriter for some reason uses writer.sheets to access the sheet.
  ## If you leave it empty it will not know that sheet Main is already there
  ## and will create a new sheet.
  writer.sheets = dict((ws.title, ws) for ws in book.worksheets)
  data_filtered.to_excel(writer, sheet_name=&quot;PCA pour intégration&quot;, index=False, startrow=2, startcol=5, header=False, verbose=True)
  writer.save()`
  </code></pre>