Python XLSX写入程序格式被其他格式禁用

给定以下代码，我的目标是将A列中的内容垂直居中。在我添加最后一段代码之前，这一切都很好，这段代码添加了底部边框，但不知何故禁用了A列的上述格式

d=pd.DataFrame({'a':['a','a','b','b'],
               'b':['a','b','c','d'],
               'c':[1,2,3,4]})
d=d.groupby(['a','b']).sum()

pd.core.format.header_style = None

writer = pd.ExcelWriter('pandas_out.xlsx', engine='xlsxwriter')
workbook  = writer.book
d.to_excel(writer, sheet_name='Sheet1')

worksheet = writer.sheets['Sheet1']

format = workbook.add_format()
format.set_align('center')
format.set_align('vcenter')
worksheet.set_column('A:C',5, format)

#This seems to disable what I have above for alignment.
formatgbs = workbook.add_format()
formatgbs.set_bottom(7)
for i in np.arange(4):
    worksheet.set_row(i,15,formatgbs)
writer.save()

有没有办法让这两个人“玩得开心”

提前谢谢