question on my reading/exercise

[MattSS102]

I followed the book (Learn Python the Hard Way) correctly and still my code gets an error. What am I doing wrong?

Error: Traceback (most recent call last):
File "ex17.py", line 4, in <module>
script, from_file, to_file = argv
ValueError: need more than 1 value to unpack

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?
in_file = open(from_file)
indata = in_file.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()

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

print "Alright, all done."

out_file.close()
in_file.close()

[Larz60+]

This has to do with the way the module is called from the command line.
it should be:
python progname.py inputIfile_name output_file_name