How to add sheet to many excel file without overwriting using python
<p>I need to write sheets to excel file(some of them are existing, but others no)
I use <code>df.groupby('mail').apply(lambda g: g.to_excel(str(g.name) + '.xlsx'), 'sheet1')</code>
I group data from exel file and want to divide it to a lot of little with different <code>mail</code>. I still have 3 <code>df</code> and I want to group it with <code>mail</code> and also add to others <code>sheet</code> to files. 
How can I do it to 50 <code>mail</code> at the same time without overwriting?</p>