Learning Python : import exists

Question

I just completed a Python exercise and wanted to create variations of it.

My question is, when using the IF/ELSE statement how can I avoid using out_file = open(to_file,'w') out_file.write(indata) twice?

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)

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

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

if exists(to_file):
    print "File already exists, override?"
    raw_input()
else:
    out_file = open(to_file,'w')
    out_file.write(indata)

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

print"Done."
    
out_file.close()
in_file.close()

I think you've stumbled upon one of the main reasons why functions exist :) — jDo
– jDo, Commented Mar 25, 2017 at 16:56
As I said, I just started to dive into the world of coding. So please, give me an example so I can learn! ;) — Vito La Manna
– Vito La Manna, Commented Mar 27, 2017 at 16:38

nb1987 · Accepted Answer · 2017-03-25 17:05:03Z

1

Currently your script doesn't genuinely consider the user's input for whether to overwrite, and you overwrite regardless of their input. It looks like you want to consider their input, so I would recommend something like:

proceed = False
if exists(to_file):
    print "File already exists, override?"
    ans = raw_input("y/n: ")
    if ans == "y":
        proceed = True
else:
    proceed = True

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

Also, you'll probably want to do some error handling if the from_file doesn't exist, as in that circumstance the call to open() will raise an IOError -- see https://docs.python.org/2/library/functions.html#open

answered Mar 25, 2017 at 17:05

nb1987

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2 Comments

erik258 Over a year ago

I like the use of proceed turn 2 nested conditions into one flag for writing the file. I also like that this answer opens the output file only if the user is going to write to it. And calling out the need to handle more errors - very nice.

Vito La Manna Over a year ago

Thank you very much. I want to consider user input only if file already exists.

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