Dynamicaly open file

Recently i had gone through a situation like to split a 40GB csv file for further processing, into 60 pieces having name/content to be decided dynamically based on a id present in that csv file. That really make me to write some little code to open/write/close file dynamically. I wrote following code to achieve this.

import os, sys
a=range(10)
for each in a:
    s = "fl_%s = open('%s','a')" % (each,each)
    exec s
    exec "fl_%s.write('%s')" % (each,each)
    com = "fl_%s.close()" % (each)
    exec com
    # can also check if file is closed or open by
    # com = "fl_%s.closed" % (each)
    # bool(com) #return true if file is closed else false