Python Palindrome Method: Detect Words, Sentences

Check words and sentences to see if they are palindromes. Use a while true loop and handle spaces and punctuation.
Palindrome. A palindrome reads the same forwards and backwards. Some common words, like "level" are palindromes. But some entire sentences are also palindromes. We can check these in Python with a simple method.Strings
Example. To check for a palindrome, we use a loop to consider the start and end characters of a string together. We move inwards until we are at the center. If both halves of the string have equal characters, we have a palindrome.

Lines: In this list, I specify an assortment of known palindromes (like "civic"). Punctuation and whitespace is included.

Maketrans: With this method, we create a dictionary to replace all punctuation with spaces. It also lowercases letters.

Translate: This method applies the dictionary created by maketrans to remove unwanted characters. Replace then eliminates spaces.

Info: We pass the reduced strings (which have no punctuation, capital letters or whitespace) to the is_palindrome method.

Python program that checks for palindromes def is_palindrome(value): min = 0 max = len(value) - 1 # Scan string for letter equality at each end. # ... Move indexes closer to the center after each check. while True: # Return true if all characters were checked. if min > max: return True; a = value[min] b = value[max] # Return false is characters are not equal. if a != b: return False; # Move inwards. min += 1 max -= 1 lines = ["civic", "A man, a plan, a canal: Panama.", "A Toyota. Race fast, safe car. A Toyota.", "Cigar? Toss it in a can. It is so tragic.", "Dammit, I'm mad!", "Delia saw I was ailed.", "Desserts, I stressed!", "Draw, O coward!", "Lepers repel.", "Live not on evil.", "Lonely Tylenol.", "Murder for a jar of red rum.", "Never odd or even.", "No lemon, no melon.", "Senile felines.", "So many dynamos!", "Step on no pets.", "Was it a car or a cat I saw?", "Dot Net Perls is not a palindrome.", "Why are you reading this?", "This article is not useful."] # Use to translate punctuation to spaces. # ... Changes uppercase to lowercase. dict = str.maketrans(",:.'!?ABCDEFGHIJKLMNOPQRSTUVWXYZ", " abcdefghijklmnopqrstuvwxyz") for line in lines: # Change all punctuation to spaces. line = line.translate(dict) # Remove all spaces. line = line.replace(" ", "") # See if line is a palindrome. if is_palindrome(line): print("Palindrome: ", line) else: print("Not palindrome:", line) Output Palindrome: civic Palindrome: amanaplanacanalpanama Palindrome: atoyotaracefastsafecaratoyota Palindrome: cigartossitinacanitissotragic Palindrome: dammitimmad Palindrome: deliasawiwasailed Palindrome: dessertsistressed Palindrome: drawocoward Palindrome: lepersrepel Palindrome: livenotonevil Palindrome: lonelytylenol Palindrome: murderforajarofredrum Palindrome: neveroddoreven Palindrome: nolemonnomelon Palindrome: senilefelines Palindrome: somanydynamos Palindrome: steponnopets Palindrome: wasitacaroracatisaw Not palindrome: dotnetperlsisnotapalindrome Not palindrome: whyareyoureadingthis Not palindrome: thisarticleisnotuseful
To detect palindromes, we scan the start and end of a string, progressing towards the center. It is possible (and possibly faster) to avoid preprocessing strings. We could modify is_palindrome to ignore non-letter characters.
A summary. We combined several Python methods, including maketrans, translate and the replace() method. Detecting palindromes is not that useful. But it helps us understand Python better. And that is useful.TranslateReplace
© 2007-2019 Sam Allen. Every person is special and unique. Send bug reports to info@dotnetperls.com.
HomeSearch
Home
Dot Net Perls