Word Games: Palindromes & Flips

12 min 30 XP

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Lesson 4 of 5 · View course roadmap

Step 1

Learn the idea

Strings hide a whole toy box. The star trick is slicing with a negative step: word[::-1] reads the string backwards.

A palindrome reads the same both ways ("racecar"). The test writes itself — but real words have capital letters, so normalise first:

word.lower() — level the playing field
word[::-1] — the reversed string
clean == clean[::-1] — the palindrome test

This normalise-then-compare pattern is everywhere in real code: case-insensitive logins, search matching, de-duplicating names. You're learning it with toys; you'll use it at work.

Where you'll use this

Normalise-then-compare powers case-insensitive logins, search engines, duplicate detection and spell checkers. DNA analysis uses the same reversal tricks on genetic sequences.

Common mistakes

Comparing without normalising case first — 'Level' != 'level' to Python.
Confusing word.reverse() (doesn't exist for strings) with the slice word[::-1].
Testing the original word instead of the cleaned one after lowering it — clean, then use the clean value everywhere.

Pro tip

For phrase palindromes ('Never odd or even'), strip non-letters first: clean = "".join(ch for ch in text.lower() if ch.isalpha()). One comprehension makes the test bulletproof.

Step 2

Try it yourself

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The lesson example is loaded and ready — press Run, then change something and run it again. Breaking it is part of learning. Want a clean slate? Tap “New blank”.

PYexample.py

⌘ + Enter to run

Output appears here…

Step 3

Pass the challenge +30 XP

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For each word in ["Level", "python", "Racecar"], print word -> palindrome! if it reads the same backwards (ignoring case), otherwise word -> not a palindrome. Keep the word's original capitalisation in the output.

Target output

Level -> palindrome!
python -> not a palindrome
Racecar -> palindrome!

PYchallenge.py

words = ["Level", "python", "Racecar"]

for word in words:
    clean = word.lower()
    if clean == clean[::-1]:
        print(f"{word} -> palindrome!")
    else:
        print(f"{word} -> not a palindrome")

Run your code to check it…

Step 4

Check your understanding

1. What does "python"[::-1] evaluate to? python nohtyp p An error

2. Why call .lower() before the palindrome test? It's required by slicing So 'Level' matches 'level' — comparisons are case-sensitive It removes spaces It reverses the string

Last step

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