python win32 COM closing excel workbook

I open several different workbooks (excel xlsx format) in COM, and mess with them. As the program progresses I wish to close one specific workbook but keep the rest open.

How do I close ONE workbook? (instead of the entire excel application)

xl = Dispatch("Excel.Application")
xl.Visible = False
try:
    output = xl.Workbooks.Open(workbookName)
    output2 = xl.Workbooks.Open(workbook2Name)
except com_error:
    print "you screwed up blahblahblah"
    exit()

#work on some stuff
#close output but keep output2 open