xlrd - append data to already opened workbook
Not directly.  xlutils can use xlrd and xlwt to copy a spreadsheet, and appending to a "to be written" worksheet is straightforward.  I don't think reading the open spreadsheet is a problem -- but xlwt will not write to the open book/sheet.
You might write an Excel VBA macro to draw the graphs.  In principle, I think a macro from a command workbook could close your stock workbook, invoke your python code to copy and update, open the new spreadsheet, and maybe run the macro to re-draw the graphs.
Another approach is to use matplotlib for the graphs.  I'd think a sleep loop could wake up every n seconds, grab the new csv data, append it to your "big" csv data, and re-draw the graph.  Taking this approach keeps you in python and should make things a lot easier, imho.  Disclosure: my Python is better than my VBA.
I am trying to write a python program for appending live stock quotes from a csv file to an excel file (which is already open) using xlrd and xlwt.
The task is summarised below.
From my stock-broker's application, a csv file is continually being updated on my hard disk.
I wish to write a program which, when run, would append the new data from csv file to an excel file, which is kept open (I wonder whether it is possible to read & write an open file).
I wish to keep the file open because I will be having stock-charts in it.
Is it possible? If yes, how?