How to check for palindrome using Python logic

Question

I m trying to check for a palindrome with Python  The code I have is very for-loop intensive   And it seems to me the biggest mistake people do when going from C to Python is trying to implement C logic using Python  which makes things run slowly  and it s just not making the most of the language   I see on this website  Search for  C-style for   that Python doesn t have C-style for loops  Might be outdated  but I interpret it to mean Python has its own methods for this   I ve tried looking around  I can t find much up to date  Python 3  advice for this  How can I solve a palindrome challenge in Python  without using the for loop   I ve done this in C in class  but I want to do it in Python  on a personal basis  The problem is from the Euler Project  great site By the way    def isPalindrome n       lst    int n  for n in str n       l len lst      if l  0    l  1          return True     elif len lst  2  0          for k in range  l                    else          while  k lt    l-1  2                if  list                               for i in range  999  100  -1       for j in range  999 100  -1           if isPalindrome i j               print i j              break   I m missing a lot of code here  The five hashes are just reminders for myself   Concrete questions    In C  I would make a for loop comparing index 0 to index max  and then index 0 1 with max-1  until something something  How to best do this in Python  My for loop  in in range  999  100  -1   is this a bad way to do it in Python  Does anybody have any good advice  or good websites  or resources for people in my position  I m not a programmer  I don t aspire to be one  I just want to learn enough so that when I write my bachelor s degree thesis  electrical engineering   I don t have to simultaneously LEARN an applicable programming language while trying to obtain good results in the project   How to go from basic C to great application of Python   that sort of thing  Any specific bits of code to make a great solution to this problem would also be appreciated  I need to learn good algorithms   I am envisioning 3 situations  If the value is zero or single digit  if it is of odd length  and if it is of even length  I was planning to write for loops      PS  The problem is  Find the highest value product of two 3 digit integers that is also a palindrome

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You are asking palindrome in python  palindrome can be performed on strings  numbers and lists  However  I just posted a simple code to check palindrome of a string     Palindrome of string str raw input  Enter the string n   ln len str  for i in range ln 2        if str ln-i-1   str i            break if i   ln 2 -1       print  Palindrome  else      print  Not Palindrome

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import string  word   input  Please select a word to test  n   word   word lower   num   len word   x   round  len word -1  2   defines first half of string first   word  x    reverse second half of string def reverse odd text       lst          count   1     for i in range x 1  len text             lst append text len text -count           count    1     lst      join lst      return lst   reverse second half of string def reverse even text       lst          count   1     for i in range x  len text            lst append text len text -count           count    1     lst      join lst      return lst   if reverse odd word     first or reverse even word     first      print string capwords word    is a palindrome   else      print string capwords word    is not a palindrome

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def isPalin checkWord       Hsize   len lst  2     seed   1     palind True     while seed lt Hsize 1           print seed lst seed-1   lst  - seed           if lst seed-1     lst  -seed                palind   False             break         seed   seed 1     return palind  lst    testset  print lst  isPalin lst      lst    testsest  print lst  isPalin lst     Output   testset True testsest False

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The awesome part of python is the things you can do with it   You don t have to use indexes for strings     The following will work  using slices   def palindrome n       return n    n   -1    What it does is simply reverses n  and checks if they are equal   n   -1  reverses n  the -1 means to decrement       2  My for loop  in in range  999  100  -1   is this a bad way to do it in Python     Regarding the above  you want to use xrange instead of range  because range will create an actual list  while xrange is a fast generator   My opinions on question 3  I learned C before Python  and I just read the docs  and played around with it using the console   and by doing Project Euler problems as well

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You can use Deques in python to check palindrome  def palindrome a string       ch dequeu   Deque       for ch in a string          ch dequeu add rear ch      still ok   True     while ch dequeu size    gt  1 and still ok          first   ch dequeu remove front           last   ch dequeu remove rear           if first    last              still ok   False         return still ok  class Deque      def   init   self           self items          def is empty self           return self items           def add rear self  item           self items insert 0  item      def add front self  item           self items append item      def size self           return len self items      def remove front self           return self items pop       def remove rear self           return self items pop 0

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A pythonic way to determine if a given value is a palindrome   str n     str n    -1    Explanation    We re checking if the string representation of n equals the inverted string representation of n The    -1  slice takes care of inverting the string After that  we compare for equality using

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maybe you can try this one       list input  enter a string     if  list  list   -1        print   It is a palindrome   else     print  it is not palindrome

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The real easy way to do that it is   word   str raw input      is palindrome   word find word   -1   if is palindrome    0      print True else      print False   And if else here just for fancy looks  The question about palindrome was on Amazon s interview for QA

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doing the Watterloo course for python  the same questions is raised as a  Lesseon  find the info here   http   cscircles cemc uwaterloo ca 13-lists   being a novice i solved the problem the following way   def isPalindrome S       pali   True     for i in range  0  len S     2           if S i     S  i   -1  - 1  and pali is True              pali   True         else              pali   False     print pali      return pali   The function is called isPalindrome S  and requires a string  S   The return value is by default TRUE  to have the initial check on the first if statement   After that  the for loop runs half the string length to check if the character from string  S  at the position  i  is the same at from the front and from the back  If once this is not the case  the function stops  prints out FALSE and returns false   Cheers kg

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If the string has an uppercase or non-alphabetic character then the function converts all characters to lowercase and removes all non-alphabetic characters using regex finally it applies palindrome check recursively   import re  rules         lambda s  any x isupper   for x in s       lambda s  not s isalpha       def is palindrome s       if any rule s  for rule in rules           s   re sub r    w        s  lower       if len s   lt  2          return True     if s 0     s -1           return False     return is palindrome s 1 -1     string    Are we not drawn onward  we few  drawn onward to new era    print is palindrome string     the output is True for the input above

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def pali str1       l list str1      l1 l   -1      if l1  l          print  yess       else          print  noo   str1  abc  a pali str1  print a

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Here a case insensitive function since all those solutions above are case sensitive    def Palindrome string       return  string upper      string upper     -1      This function will return a boolean value

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def is palindrome string      return string       join  letter for letter in reversed string

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it is very easy   palindrome a raw input  enter the word   b a   -1  if a  b   print  enter word is palindrome   else  enter code here   print  not a palindrome     thanks

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word     lt insert palindrome string gt   reverse   word   -1   is palindrome   word find reverse  print is palindrome   This was a question in Udacity comp 101  chapter 1  Gives a 0 for palindrome gives a -1 for not  Its simple  and does not use loops

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the  algorithmic  way   import math  def isPalindrome inputString       if inputString    None          return False      strLength   len inputString      for i in range math floor strLength            if inputString i     inputString strLength - 1 - i               return False     return True

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I know that this question was answered a while ago and i appologize for the intrusion  However I was working on a way of doing this in python as well and i just thought that i would share the way that i did it in is as follows  word    aibohphobia   word rev   reversed word   def is palindrome word       if list word     list word rev           print True  it is a palindrome      else          print False  this is  t a plindrome   is palindrome word

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There is much easier way I just found  It s only 1 line   is palindrome   word find word   -1

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I tried using this   def palindrome numer num   num str   str num  str list   list num str  if str list 0     str list -1       return True return False   and it worked for a number but I don t know if a string

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It looks prettier with recursion   def isPalindrome x   z   numToList x  length   math floor len z    2  if length  lt  2      if z 0     z -1           return True     else          return False else      if z 0     z -1           del z 0          del z -1          return isPalindrome z      else          return False

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print   Not a palindrome   Is a palindrome   s       join  s len s -i-1  for i in range len s        This is the typical way of writing single line code

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Here is an example that takes a user s input and checks if the input is a palindrome   name   input  Write your word here      input  Press  lt enter gt  to check if the word is a palindrome    if str name     str name    -1       print  True   else      print  False     However  there is no need to even set up the if else statement  You can directly print the result of the logical comparison  as shown here   name   input  Write your word here      input  Press  lt enter gt  to check if the word is a palindrome    print str name     str name    -1

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Assuming a string  s   palin   lambda s  s   len s  2    0 if len s  2  0 else 1   1     s  len s  2-1 -1      Test palin  654456      True palin  malma       False palin  ab1ba       True

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Below the code will print 0 if it is Palindrome else it will print -1  Optimized Code  word    nepalapen  is palindrome   word find word   -1   print is palindrome   Output  0  word    nepalapend  is palindrome   word find word   -1   print is palindrome   Output  -1  Explaination   when searching the string the value that is returned is the value of the location that the string starts at   So when you do word find word   -1   it finds nepalapen at location 0 and    -1  reverses nepalapen and it still is nepalapen at location 0 so 0 is returned    Now when we search for nepalapend and then reverse nepalapend to dnepalapen it renders a FALSE statement nepalapend was reversed to dnepalapen causing the search to fail to find nepalapend resulting in a value of -1 which indicates string not found     Another method print true if palindrome else print false  word    nepalapen  print word   -1   word   1     output  TRUE

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Just for the record  and for the ones looking for a more algorithmic way to validate if a given string is palindrome  two ways to achieve the same  using while and for loops    def is palindrome word        letters   list word          is palindrome   True     i   0      while len letters   gt  0 and is palindrome                 if letters 0     letters  len letters  - 1                is palindrome   False         else              letters pop 0              if len letters   gt  0                  letters pop  len letters  - 1        return is palindrome   And    the second one   def is palindrome word        letters   list word      is palindrome   True      for letter in letters          if letter    letters -1               letters pop -1          else              is palindrome   False             break      return is palindrome

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I wrote this code   word   input  enter     word      join word split     for x in range len word    if list word  x       list word  len word -x-1     if x 1    len word   print  its pali     and it works  it gets the word  then removes the spaces and turns it into a list then it tests if the first letter is equal to the last and if the 2nd is equal to 2nd last and so on   then the  if x 1    len word   means that since x starts at 0 it becomes 1 and then for every next    blah blah blah it works so it works

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compare 1st half with reversed second half   i e   abba  - gt   ab      ba    -1   def is palindrome  s       return True if len  s    lt  2 else s   len  s      2      s  -  len  s      2       -1

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There is also a functional way   def is palindrome word     if len word     1  return True   if word 0     word -1   return False   return is palindrome word 1 -1

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An alternative to the rather unintuitive    -1  syntax is this    gt  gt  gt  test    abcba   gt  gt  gt  test       join reversed test   True   The reversed function returns a reversed sequence of the characters in test      join   joins those characters together again with nothing in between

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There is another way by using functions  if you don t want to use reverse     usr bin python  A    kayak   def palin A        i   0     while  i lt   A   len    -1            if  A A   len    -i-1     A i                i   1         else           return False  if palin A     False       print  Not a Palindrome    else        print   Palindrome

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usr bin python  str   raw input  Enter a string    print  String entered above is  s   str strlist    x for x in str   print  Strlist is  s   strlist strrev   list reversed strlist    print  Strrev is  s   strrev if strlist    strrev      print  String is palindrome  else      print  String is not palindrome

[python] How to check for palindrome using Python logic

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