Palindrome problem - Trying to check 2 lists for equality python3.9-CodePudding

I'm writing a program to check if a given user input is a palindrome or not. if it is the program should print "Yes", if not "no". I realize that this program is entirely too complex since I actually only needed to check the whole word using the reversed() function, but I ended up making it quite complex by splitting the word into two lists and then checking the lists against each other.

Despite that, I'm not clear why the last conditional isn't returning the expected "Yes" when I pass it "racecar" as an input. When I print the lists in line 23 and 24, I get two lists that are identical, but then when I compare them in the conditional, I always get "No" meaning they are not equal to each other. can anyone explain why this is? I've tried to convert the lists to strings but no luck.

def odd_or_even(a):  # function for determining if odd or even
    if len(a) % 2 == 0:
        return True
    else:
        return False

the_string = input("How about a word?\n")
x = int(len(the_string))

odd_or_even(the_string)  # find out if the word has an odd or an even number of characters

if odd_or_even(the_string) == True:    # if even                     
    for i in range(x):
        first_half = the_string[0:int((x/2))]  #create a list with part 1
        second_half = the_string[(x-(int((x/2)))):x]  #create a list with part 2
else: #if odd
    for i in range(x):
        first_half = the_string[:(int((x-1)/2))] #create a list with part 1 without the middle index
        second_half = the_string[int(int(x-1)/2) 1:] #create a list with part 2 without the middle index

print(list(reversed(second_half)))
print(list(first_half))

if first_half == reversed(second_half):  ##### NOT WORKING BUT DONT KNOW WHY #####
    print("Yes")
else:
    print("No")

CodePudding user response：

Despite your comments first_half and second_half are substrings of your input, not lists. When you print them out, you're converting them to lists, but in the comparison, you do not convert first_half or reversed(second_half). Thus you are comparing a string to an iterator (returned by reversed), which will always be false.

So a basic fix is to do the conversion for the if, just like you did when printing the lists out:

if list(first_half) == list(reversed(second_half)):

A better fix might be to compare as strings, by making one of the slices use a step of -1, so you don't need to use reversed. Try second_half = the_string[-1:x//2:-1] (or similar, you probably need to tweak either the even or odd case by one). Or you could use the "alien smiley" slice to reverse the string after you slice it out of the input: second_half = second_half[::-1].

There are a few other oddities in your code, like your for i in range(x) loop that overwrites all of its results except the last one. Just use x - 1 in the slicing code and you don't need that loop at all. You're also calling int a lot more often than you need to (if you used // instead of /, you could get rid of literally all of the int calls).