Szathmáry László honlapja @ DEIK

a-z; with reversed source code: z-a

Write a Python script that prints the lower case letters of the English alphabet from a to z.

Now reverse the source code of the script. The reversed source should also give a valid Python script, and if you run it, you should get the lower case letters of the English alphabet in a reversed way from z to a.

Tip: pass your Python script to the Python interpreter, as seen below in the running example.

To reverse a file, use this program (reverse.py):

#!/usr/bin/env python

import sys

def main():
with open(sys.argv[1]) as f:
print f.read()[::-1]

##############################################################

if __name__ == "__main__":
if len(sys.argv) == 1:
print "One parameter is required."
sys.exit(1)
# else
main()

Running example:

$ ls -al
total 20
drwxrwxr-x 2 jabba jabba 4096 Sep 19 13:31 .
drwxrwxr-x 3 jabba jabba 4096 Sep 19 13:26 ..
-rwx------ 1 jabba jabba  124 Sep 19 13:31 a-z.py
-rwx------ 1 jabba jabba  313 Sep 19 13:22 reverse.py
$ python ./a-z.py 
abcdefghijklmnopqrstuvwxyz
$ ./reverse.py a-z.py >back.py 
$ ls -al
total 20
drwxrwxr-x 2 jabba jabba 4096 Sep 19 13:31 .
drwxrwxr-x 3 jabba jabba 4096 Sep 19 13:26 ..
-rwx------ 1 jabba jabba  124 Sep 19 13:31 a-z.py
-rw-rw-r-- 1 jabba jabba  125 Sep 19 13:31 back.py
-rwx------ 1 jabba jabba  313 Sep 19 13:22 reverse.py
$ python back.py 
zyxwvutsrqponmlkjihgfedcba
$

The file "back.py" may be 1 byte longer. It is due to an extra newline character.

20130919b