Setting quotePrefix flag
*Created originally on Bitbucket by [newgarden (Newgarden)](https://bitbucket.org/%7B42c9e9a7-659d-4d56-a828-60b091a5d005%7D/)* MS Excel application allows to escape cell values starting with "=", "+", "-", "@" etc. by adding a single quote character (') at the beginning of the string, which prevents treating the value as a formula. The quote character is visible in the formula bar but not in the cell. When the file saved as an xlsx workbook, the quote is not stored as part of the cell value, but as *quotePrefix* flag. It would be nice if openpyxl provides a way to mimic this behavior when writing and saving a workbook. The primary use case is escaping potentially malicious content during file generation from an application. The Cell class has the *quotePrefex* property. This attribute can be read but cannot be updated. This works ``` #!python wb = load_workbook(filename='test.xlsx') s = wb.worksheets[0] is_escaped = ['A1'].quotePrefix ``` This would be nice to have ``` #!python wb = Workbook() ws = wb.active ws['A1'] = "cmd malicious_app" ws['A1'].quotePrefix = True wb.save('test.xlsx') ``` This issue has been brought up in the mailing list and StackOverflow: https://groups.google.com/d/msg/openpyxl-users/Z4QBuFYtMo0/VIkcmGszBQAJ https://stackoverflow.com/questions/50027429/openpyxl-how-to-put-value-with-a-leading-single-quote
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