anup@ashendkar-Ub-in:~/programs/python$ python ex17.py ex15_sample.txt abc.txt 
Copying from ex15_sample.txt to abc.txt
The input file is 21 bytes long
Does the output file exist? True
Ready, hit RETURN to continue, CTRL-C to abort.

Alright, all done.
anup@ashendkar-Ub-in:~/programs/python$ cat abc.txt 
anup 
ashok
shenkdar
anup@ashendkar-Ub-in:~/programs/python$ cat ex15_sample.txt 
anup 
ashok
shenkdar
anup@ashendkar-Ub-in:~/programs/python$ cat ex17.py 
from sys import argv
from os.path import exists

script, from_file, to_file = argv

print "Copying from %s to %s" % (from_file, to_file)

# we could do these two on one line too, how?
input = open(from_file)
indata = input.read()

print "The input file is %d bytes long" % len(indata)

print "Does the output file exist? %r" % exists(to_file)
print "Ready, hit RETURN to continue, CTRL-C to abort."
raw_input()

output = open(to_file, 'w')
output.write(indata)

print "Alright, all done."

output.close()
input.close()

anup@ashendkar-Ub-in:~/programs/python$