Python: Find all even palindromes up to n

Last update on May 28 2022 13:41:42 (UTC/GMT +8 hours)

Python Programming Puzzles: Exercise-45 with Solution

From Wikipedia,
A palindromic number (also known as a numeral palindrome or a numeric palindrome) is a number (such as 16461) that remains the same when its digits are reversed. In other words, it has reflectional symmetry across a vertical axis. The term palindromic is derived from palindrome, which refers to a word (such as rotor or racecar) whose spelling is unchanged when its letters are reversed. The first 30 palindromic numbers (in decimal) are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, ...

Write a Python program to find all even palindromes up to n.

Output:
Even palindromes up to 50 -
[0, 2, 4, 6, 8, 22, 44]

Even palindromes up to 100 -
[0, 2, 4, 6, 8, 22, 44, 66, 88]

Even palindromes up to 500 -
[0, 2, 4, 6, 8, 22, 44, 66, 88, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494]

Even palindromes up to 2000 -
[0, 2, 4, 6, 8, 22, 44, 66, 88, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 606, 616, 626, 636, 646, 656, 666, 676, 686, 696, 808, 818, 828, 838, 848, 858, 868, 878, 888, 898]

Sample Solution:

Python Code:

#License: https://bit.ly/3oLErEI

def test(n):
    return [i for i in range(0,n,2) if str(i) == str(i)[::-1]] 
n = 50
print("\nEven palindromes up to",n,"-")
print(test(n))
n = 100
print("\nEven palindromes up to",n,"-")
print(test(n))
n = 500
print("\nEven palindromes up to",n,"-")
print(test(n))
n = 2000
print("\nEven palindromes up to",n,"-")
print(test(n))

Sample Output:

Even palindromes up to 50 -
[0, 2, 4, 6, 8, 22, 44]

Even palindromes up to 100 -
[0, 2, 4, 6, 8, 22, 44, 66, 88]

Even palindromes up to 500 -
[0, 2, 4, 6, 8, 22, 44, 66, 88, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494]

Even palindromes up to 2000 -
[0, 2, 4, 6, 8, 22, 44, 66, 88, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 606, 616, 626, 636, 646, 656, 666, 676, 686, 696, 808, 818, 828, 838, 848, 858, 868, 878, 888, 898]

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Previous: Determine which characters of a hexadecimal number correspond to prime numbers.
Next: Find the minimum even value and its index from a given array of numbers.

Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

The os and os.path modules.

The __file__ constant

os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")

os.path.dirname(path) (returns "the directory name of pathname path")

os.getcwd() (returns "a string representing the current working directory")

os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m