Python: search longest palindromes within a word and palindromes within a word/string

So here is a code i have written to find palindromes within a word (To check if there are palindromes within a word including the word itself) Condition: spaces inbetween characters are counted and not ignored Example: A but tuba is a palindrome but technically due to spaces involved now it isn’t. so that’s the criteria.

Based on above, the following code usually should work. You can try on your own with different tests to check out if this code gives any error.

def pal(text):
    """

    param text: given string or test
    return: returns index of longest palindrome and a list of detected palindromes stored in temp
    """
    lst = {}
    index = (0, 0)
    length = len(text)
    if length <= 1:
        return index
    word = text.lower()  # Trying to make the whole string lower case
    temp = str()
    for x, y in enumerate(word):
        # Try to enumerate over the word
        t = x
        for i in xrange(x):
            if i != t+1:
                string = word[i:t+1]
                if string == string[::-1]:
                    temp = text[i:t+1]
                    index = (i, t+1)
                    lst[temp] = index
    tat = lst.keys()
    longest = max(tat, key=len)
    #print longest
    return lst[longest], temp

And here is a defunct version of it. What I mean is I have tried to start out from the middle and detect palindromes by iterating from the beginning and checking for each higher and lower indices for character by checking if they are equal characters. if they are then i am checking if its a palindrome like a regular palindrome check. here’s what I have done

def pal(t):
    text = t.lower()
    lst = {}
    ptr = ''
    index = (0, 0)
    #mid = len(text)/2
    #print mid
    dec = 0
    inc = 0
    for mid, c in enumerate(text):
        dec = mid - 1
        inc = mid + 1
        while dec != 0 and inc != text.index(text[-1]):
            print 'dec {}, inc {},'.format(dec, inc)
            print 'text[dec:inc+1] {}'.format(text[dec:inc+1])
            if dec<0:
                dec = 0
            if inc > text.index(text[-1]):
                inc = text.index(text[-1])
            while text[dec] != text[inc]:
                flo = findlet(text[inc], text[:dec])
                fhi = findlet(text[dec], text[inc:])
                if len(flo) != 0 and len(fhi) != 0 and text[flo[-1]] == text[fhi[0]]:
                    dec = flo[-1]
                    inc = fhi[0]
                    print ' break if'
                    break
                elif len(flo) != 0 and text[flo[-1]] == text[inc]:
                    dec = flo[-1]
                    print ' break 1st elif'
                    break
                elif len(fhi) != 0 and text[fhi[0]] == text[inc]:
                    inc = fhi[0]
                    print ' break 2nd elif'
                    break
                else:
                    dec -= 1
                    inc += 1
                    print ' break else'
                    break
            s = text[dec:inc+1]
            print ' s {} '.format(s)
            if s == s[::-1]:
                index = (dec, inc+1)
                lst[s] = index
            if dec > 0:
                dec -= 1
            if inc < text.index(text[-1]):
                inc += 1
    if len(lst) != 0:
        val = lst.keys()
        longest = max(val, key = len)
        return lst[longest], longest, val
    else:
        return index

findlet() fun:

def findlet(alpha, string):
    f = [i for i,j in enumerate(string) if j == alpha]
    return f

Sometimes it works:

pal('madem')
dec -1, inc 1,
text[dec:inc+1] 
 s m 
dec 1, inc 3,
text[dec:inc+1] ade
 break 1st elif
 s m 
dec 2, inc 4,
text[dec:inc+1] dem
 break 1st elif
 s m 
dec 3, inc 5,
text[dec:inc+1] em
 break 1st elif
 s m 
Out[6]: ((0, 1), 'm', ['m'])

pal('Avid diva.')
dec -1, inc 1,
text[dec:inc+1] 
 break 2nd if
 s avid div 
dec 1, inc 3,
text[dec:inc+1] vid
 break else
 s avid  
dec 2, inc 4,
text[dec:inc+1] id 
 break else
 s vid d 
dec 3, inc 5,
text[dec:inc+1] d d
 s d d 
dec 2, inc 6,
text[dec:inc+1] id di
 s id di 
dec 1, inc 7,
text[dec:inc+1] vid div
 s vid div 
dec 4, inc 6,
text[dec:inc+1]  di
 break 1st elif
 s id di 
dec 1, inc 7,
text[dec:inc+1] vid div
 s vid div 
dec 5, inc 7,
text[dec:inc+1] div
 break 1st elif
 s vid div 
dec 6, inc 8,
text[dec:inc+1] iva
 break 1st elif
 s avid diva 
dec 8, inc 10,
text[dec:inc+1] a.
 break else
 s va. 
dec 6, inc 10,
text[dec:inc+1] iva.
 break else
 s diva. 
dec 4, inc 10,
text[dec:inc+1]  diva.
 break else
 s d diva. 
dec 2, inc 10,
text[dec:inc+1] id diva.
 break else
 s vid diva. 
Out[9]: ((0, 9), 'avid diva', ['avid diva', 'd d', 'id di', 'vid div'])

And based on the Criteria/Condition i have put:

pal('A car, a man, a maraca.')
dec -1, inc 1,
text[dec:inc+1] 
 break else
 s  
dec -1, inc 3,
text[dec:inc+1] 
 s a ca 
dec 1, inc 3,
text[dec:inc+1]  ca
 break if
 s a ca 
dec 2, inc 4,
text[dec:inc+1] car
 break else
 s  car, 
dec 3, inc 5,
text[dec:inc+1] ar,
 break else
 s car,  
dec 1, inc 7,
text[dec:inc+1]  car, a
 break 1st elif
 s a car, a 
dec 4, inc 6,
text[dec:inc+1] r, 
 break 1st elif
 s  car,  
dec 5, inc 7,
text[dec:inc+1] , a
 break 1st elif
 s ar, a 
dec 2, inc 8,
text[dec:inc+1] car, a 
 break 1st elif
 s  car, a  
dec 6, inc 8,
text[dec:inc+1]  a 
 s  a  
dec 5, inc 9,
text[dec:inc+1] , a m
 break else
 s r, a ma 
dec 3, inc 11,
text[dec:inc+1] ar, a man
 break else
 s car, a man, 
dec 1, inc 13,
text[dec:inc+1]  car, a man, 
 s  car, a man,  
dec 7, inc 9,
text[dec:inc+1] a m
 break else
 s  a ma 
dec 5, inc 11,
text[dec:inc+1] , a man
 break else
 s r, a man, 
dec 3, inc 13,
text[dec:inc+1] ar, a man, 
 break if
 s   
dec 8, inc 10,
text[dec:inc+1]  ma
 break if
 s  
dec 6, inc 4,
text[dec:inc+1] 
 break 1st elif
 s r 
dec 3, inc 5,
text[dec:inc+1] ar,
 break else
 s car,  
dec 1, inc 7,
text[dec:inc+1]  car, a
 break 1st elif
 s a car, a 
dec 9, inc 11,
text[dec:inc+1] man
 break else
 s  man, 
dec 7, inc 13,
text[dec:inc+1] a man, 
 break if
 s  
dec 5, inc 2,
text[dec:inc+1] 
 break 1st elif
 s c 
dec 1, inc 3,
text[dec:inc+1]  ca
 break if
 s a ca 
dec 10, inc 12,
text[dec:inc+1] an,
 break 1st elif
 s , a man, 
dec 4, inc 13,
text[dec:inc+1] r, a man, 
 break 1st elif
 s  car, a man,  
dec 11, inc 13,
text[dec:inc+1] n, 
 break 1st elif
 s  man,  
dec 7, inc 14,
text[dec:inc+1] a man, a
 s a man, a 
dec 6, inc 15,
text[dec:inc+1]  a man, a 
 s  a man, a  
dec 5, inc 16,
text[dec:inc+1] , a man, a m
 break else
 s r, a man, a ma 
dec 3, inc 18,
text[dec:inc+1] ar, a man, a mar
 break else
 s car, a man, a mara 
dec 1, inc 20,
text[dec:inc+1]  car, a man, a marac
 break else
 s a car, a man, a maraca 
dec 12, inc 14,
text[dec:inc+1] , a
 break 1st elif
 s an, a 
dec 9, inc 15,
text[dec:inc+1] man, a 
 break if
 s  
dec 7, inc 2,
text[dec:inc+1] 
 break 1st elif
 s c 
dec 1, inc 3,
text[dec:inc+1]  ca
 break if
 s a ca 
dec 13, inc 15,
text[dec:inc+1]  a 
 s  a  
dec 12, inc 16,
text[dec:inc+1] , a m
 break 1st elif
 s man, a m 
dec 8, inc 17,
text[dec:inc+1]  man, a ma
 break 1st elif
 s a man, a ma 
dec 6, inc 18,
text[dec:inc+1]  a man, a mar
 break 1st elif
 s r, a man, a mar 
dec 3, inc 19,
text[dec:inc+1] ar, a man, a mara
 s ar, a man, a mara 
dec 2, inc 20,
text[dec:inc+1] car, a man, a marac
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 14, inc 16,
text[dec:inc+1] a m
 break 1st elif
 s man, a m 
dec 8, inc 17,
text[dec:inc+1]  man, a ma
 break 1st elif
 s a man, a ma 
dec 6, inc 18,
text[dec:inc+1]  a man, a mar
 break 1st elif
 s r, a man, a mar 
dec 3, inc 19,
text[dec:inc+1] ar, a man, a mara
 s ar, a man, a mara 
dec 2, inc 20,
text[dec:inc+1] car, a man, a marac
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 15, inc 17,
text[dec:inc+1]  ma
 break 1st elif
 s a ma 
dec 13, inc 18,
text[dec:inc+1]  a mar
 break 1st elif
 s r, a man, a mar 
dec 3, inc 19,
text[dec:inc+1] ar, a man, a mara
 s ar, a man, a mara 
dec 2, inc 20,
text[dec:inc+1] car, a man, a marac
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 16, inc 18,
text[dec:inc+1] mar
 break 1st elif
 s r, a man, a mar 
dec 3, inc 19,
text[dec:inc+1] ar, a man, a mara
 s ar, a man, a mara 
dec 2, inc 20,
text[dec:inc+1] car, a man, a marac
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 17, inc 19,
text[dec:inc+1] ara
 s ara 
dec 16, inc 20,
text[dec:inc+1] marac
 break 1st elif
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 18, inc 20,
text[dec:inc+1] rac
 break 1st elif
 s car, a man, a marac 
dec 1, inc 21,
text[dec:inc+1]  car, a man, a maraca
 break 1st elif
 s a car, a man, a maraca 
dec 19, inc 21,
text[dec:inc+1] aca
 s aca 
dec 21, inc 23,
text[dec:inc+1] a.
 break else
 s ca. 
dec 19, inc 23,
text[dec:inc+1] aca.
 break else
 s raca. 
dec 17, inc 23,
text[dec:inc+1] araca.
 break else
 s maraca. 
dec 15, inc 23,
text[dec:inc+1]  maraca.
 break else
 s a maraca. 
dec 13, inc 23,
text[dec:inc+1]  a maraca.
 break else
 s , a maraca. 
dec 11, inc 23,
text[dec:inc+1] n, a maraca.
 break else
 s an, a maraca. 
dec 9, inc 23,
text[dec:inc+1] man, a maraca.
 break else
 s  man, a maraca. 
dec 7, inc 23,
text[dec:inc+1] a man, a maraca.
 break else
 s  a man, a maraca. 
dec 5, inc 23,
text[dec:inc+1] , a man, a maraca.
 break else
 s r, a man, a maraca. 
dec 3, inc 23,
text[dec:inc+1] ar, a man, a maraca.
 break else
 s car, a man, a maraca. 
dec 1, inc 23,
text[dec:inc+1]  car, a man, a maraca.
 break else
 s a car, a man, a maraca. 
Out[8]: ((13, 16), ' a ', ['', ' a ', 'c', ' ', 'aca', 'ara', 'r'])

Sometimes, it doesn’t work at all:

    pal('madam')
    dec -1, inc 1,
    text[dec:inc+1] 
     s m 
    dec 1, inc 3,
    text[dec:inc+1] ada
     break 1st elif
     s m 
    dec 2, inc 4,
    text[dec:inc+1] dam
     break 1st elif
     s m 
    dec 3, inc 5,
    text[dec:inc+1] am
     break 1st elif
     s m 
    Out[5]: ((0, 1), 'm', ['m'])

Now considering madam is a very nice palindrome it should work and there are many cases which i haven’t tested myself to find out what other legitimate palindromes it doesn’t detect.

Q1: Why is it sometimes not detecting?

Q2: I would like to optimize my second code for that matter. Any inputs?

Q3: What better approach is there for a much much more efficient code than my First code which iterates many a times?

Answer

Your solution seems a bit complicated to me. Just look at all of the possible substrings and check them individually:

def palindromes(text):
    text = text.lower()
    results = []

    for i in range(len(text)):
        for j in range(0, i):
            chunk = text[j:i + 1]

            if chunk == chunk[::-1]:
                results.append(chunk)

    return text.index(max(results, key=len)), results

text.index() will only find the first occurrence of the longest palindrome, so if you want the last, replace it with text.rindex().