Learn Python the Hard Way Exercise 17 Extra Question(S)

Question

I'm doing Zed Shaw's fantastic Learn Python The Hard Way, but an extra question has me stumped: Line 9--10 could be written in one line, how? I've tried some different thoughts, but to no avail. I could move on, but what would the fun in that be?

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."

Zed also writes that he could do the whole script in one line. I'm not exactly sure what he means by that.

Feel free to help me however you want: by giving the answer or merely hinting---and perhaps including a collapsed or hidden answer to the question.

Answer 1

indata = open(from_file).read()

Answer 2

shutil is the way to do one-liner file copies in Python:

shutil.copy(sys.argv[1], sys.argv[2])

Putting the import shutil, sys on the same line as this one (with a semicolon in-between, of course) would however be stylistically goofy;-).

Answer 3

Well you can just do "algebraic substitution," right? ...assuming you don't care about the "UI"...

open(to_file, 'w').write(open(from_file).read())

Answer 4

I agree with the algebraic substitution mentioned by @dash-tom-bang. My functioning Exercise 17 extra credit has 5 lines. The operation is being conducted on one line.

open(to_file, 'w').write(open(from_file).read())

followed by a simple 'print' for verification feedback

print "File %s copied to %s" % (from_file, to_file)

I should have a 6th line that replaces the original ''output.close'' but I am confused about how to do this without the ''output'' variable? Ahh, since I now have no output variable there is nothing to close.

btw- It is a little spooky for me to see the same exact line typed here that I have worked out and entered myself in gedit. Great stuff, I am really enjoying the mental challenge and community support.

Edit:answered my own question