使用Python的xlsxwriter在Excel中字符串条件格式“等于”

I have relatively big Excel spreadsheets, where I am applying conditional formatting. However, the content of a cell is relatively short (max 3 letters). So, I need to match exactly a string. For example: 'A' should be formatted but nothing more containing 'A' ('ABC', 'BCA', 'BAC', etc.).I have relatively big Excel spreadsheets, where