There is no filename if you open a new excel application ...
You open a new file this way excel.Workbooks.Open(Filename,ReadOnly)
And this is for checking sheet name
import win32com.client
excel = win32com.client.Dispatch('Excel.Application')
wb = excel.Workbooks.Add()
ws = wb.Sheets(1)
if ws.Name!="TheSheetImLookingFor":
raise ValueError(ws.Name)