CODEWITHSUNDEEP
pythonpython-3.xalgorithmpalindrome
HenSinai
HenSinai

Reputation: 25

Palindrome comparison doesn't detect some cases

I want to print True if the word/line is a palindrome. The code reads the text from the text file (using sys.argv[1]). I don't understand why it's only checks the first line.

text file:

racecar
AddE
HmllpH
Was it a car or a cat I saw
Hannah
T can arise in context where language is played wit
Able was I ere I saw Elba
Doc note I dissent A fast never prevents a fatness I diet on cod

code:

import sys
filename = sys.argv[1]

with open(filename, "r") as f:
    text = f.readline().strip().lower()

    while text:
        palindrome = True
        i = 0
        while i < len(text) / 2:
            if text[i] != text[len(text) - 1 - i]:
                palindrome = False
            i += 1
        if palindrome:
            print(True)
        text = f.readline().strip()

output:

True

Upvotes: 1

Views: 57

Answers (2)

Aviv Yaniv
Aviv Yaniv

Reputation: 6298

  1. Why only the first line printed?

Only the first line is a case-sensitive palindrome.

  1. Code Fix:

Some explanation on what you see:

2.1. The loop for text in map(str.strip, f), means that we are going over file f lines and apply the str.strip() method on each of them.

2.2. text.upper() to convert text to unified upper case, for common comparison.

2.3. text_upper[::-1] to reverse text: The strange [::-1] index notation, means that we are going on all elements backward one step (therefore the -1).

import sys
filename = 'outfile.txt'

with open(filename, "r") as f:
    for text in map(str.strip, f):
        text_upper = text.upper()
        if text_upper == text_upper[::-1]:
            print(f'{text} is palindrom!')

Upvotes: 3

melbok
melbok

Reputation: 95

It does check all lines, but only the first case returns True because the other lines don't have .lower(). You would have to change the last line to text = f.readline().strip().lower().

Upvotes: 0

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