Palindrome

A palindrome is a word that reads the same forwards and backwards. racecar, madam, level: flip them around and they're the same

How do we check if a word is a palindrome? The simplest approach: reverse it and compare

word = "racecar"
if word == word[::-1]:
    print("Palindrome!")
else:
    print("Not a palindrome")

Output Palindrome!

That's it. One line of logic. We reverse the string and check if it's the same as the original. Python makes this absurdly simple

But let's also think about how to do this without the slicing trick, because the logic is important

A palindrome means: the first character equals the last, the second equals the second-to-last, and so on

def is_palindrome(word):
    for i in range(len(word) // 2):
        if word[i] != word[len(word) - 1 - i]:
            return False
    return True

print(is_palindrome("racecar"))
print(is_palindrome("hello"))
print(is_palindrome("madam"))

Output

True
False
True

We only need to check half the string. Why? Because if the first half matches the second half (mirrored), we're done. Checking the other half would be redundant

len(word) // 2 gives us half the length (integer division). For "racecar" (7 letters), we check positions 0, 1, 2 (comparing with 6, 5, 4)

What about sentences? "A man a plan a canal Panama" is a palindrome if we ignore spaces and capitalization

def is_palindrome_sentence(text):
    cleaned = ""
    for char in text:
        if char.isalpha():
            cleaned += char.lower()
    return cleaned == cleaned[::-1]

print(is_palindrome_sentence("A man a plan a canal Panama"))
print(is_palindrome_sentence("racecar"))
print(is_palindrome_sentence("hello world"))

Output

True
True
False

We first clean the string: keep only letters and convert to lowercase. Then check if it's a palindrome. Step by step, just like we learned in the decomposition lesson

Mission: Signal Integrity Check

A signal code is only trustworthy if it reads the same forwards and backwards: a palindrome. The station logged a batch of codes in a list named codes and needs them checked.

Write a function is_palindrome(word) that returns True if the word is a palindrome, False otherwise. Use a loop (compare the first letter with the last, the second with the second-to-last, ...), not [::-1].
For each code, print the code, then : , then the result.
Count how many codes are palindromes and print Valid signals: followed by that count.

Output

racecar: True
signal: False
level: True
orbit: False
radar: True
Valid signals: 3