Question

I’m reading Zed Shaw’s “Learn Python The Hard Way”. I’m up to exercise 17 ( http://learnpythonthehardway.org/book/ex17.html ) and hit the wall on extra credit #’s 2 & 3. Zed wants me to shorten the script by eliminating anything that isn’t necessary (he claims he can get it to run with just one line in the script).

Here is the original script…

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()

Here’s what I was able to shorten the script to and still get it to run properly (by properly I mean that the script successfully copies the intended text to the intended file)…

from sys import argv
from os.path import exists

script, from_file, to_file = argv

input = open (from_file)
indata = input.read ()

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

I got rid of the print commands and the two close commands (please excuse if I’m using “command” incorrectly…I’m painfully new to coding and haven’t gotten the jargon down yet).

Anything else I try to further shorten the script produces errors. For example, I tried to combine the “input” and “indata” commands into one line like so…

input = open (from_file, 'r')

Then I changed any “indata” references in the script to “input”…

from sys import argv
from os.path import exists

script, from_file, to_file = argv

input = open (from_file, 'r')

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

But I get the following TypeError…

new-host:python Eddie$ python ex17.py text.txt copied.txt
Traceback (most recent call last):
  File "ex17.py", line 10, in <module>
    output.write (input)
TypeError: expected a character buffer object

How would you go about shortening the script further…or shortening it down to just one line, as Zed suggests he can do?

Answer 1

from sys import argv
open(argv[2], 'w').write(open(argv[1]).read())

is about as short as you can get that. You could use a semicolon to join them into one line, but that’s just replacing a end-of-line character with something else and not really useful.