Palindrome-inize a number

Question

For example if I start with the number 146. I first reverse it, so it becomes 641. Then I add this to the original number to make 787 which is a palindrome. I would repeat the process if the answer is not a palindrome.

I made this program show how long it ran for when it finishes or is interrupted and also to write the output to a file called output.txt.

from sys import exit
from signal import SIGINT, signal
from timeit import default_timer


def n(x):

    counter = 0
    b = 0
    start = default_timer()

    def t(*args):

        end = default_timer()
        total = end - start
        print (total)

        with open('output.txt','w') as f:

            f.write('{}\n{}\n{}'.format(b, counter, total))

        exit(0)

    signal(SIGINT,t)


    while True:

        b += int(str(x)[::-1])

        if b == int(str(b)[::-1]):

            end = default_timer()
            print (b, counter)
            t()
            break

        else:

            counter += 1
            print (b,counter)
            x = b

Answer 1

A few notes:

• A more pythonic way to determine if a given value is a palindrome:

  str(n) == str(n)[::-1]
  

  You do something similar in your code, but are converting from a string back to an int. This is more readable to me.

  However, this can slow down the code if we do this sort of casting a lot, so it would be better to abstract this functionality to a loop to reduce the number of casts and further increase readablity:

  def is_palindrome(num):
      string = str(num)
      return string == string[::-1]
  

• Use the palindrome test as a check with the while loop

• In the while loop, use the logic you already have to add on a reversed int:

  n += int(str(n)[::-1])
  

• I would make it easier to input a number for the code to use, I did this with argparse.

  def get_args():
      parser = argparse.ArgumentParser(description=
          'Generate palindrome from number when added to its reverse')
      parser.add_argument('num', type=int, help='number for palindrome generator')
      return parser.parse_args()
  

• Right now you are writing just a snippet of data to a file, but it is being overwritten every time. I'd recommend just outputting to stdout with this current method, or changing it so you append to a file instead of overwrite it. I've gone with the former recommendation in my final code.

• For profiling and timing code, it's recommended you use a Python profiler instead of writing code yourself.

---

Final Code

import argparse


def get_args():
    parser = argparse.ArgumentParser(description=
        'Generate palindrome from number when added to its reverse')
    parser.add_argument('num', type=int, help='number for palindrome generator')
    return parser.parse_args()


def is_palindrome(num):
    string = str(num)
    return string == string[::-1]


def main():
    args = get_args()
    while not is_palindrome(args.num):
        args.num += int(str(args.num)[::-1])

    return args.num


if __name__ == "__main__":
    print(main())

Test run:

$ python test.py 146
787