Caesar Cipher Function in Python

Question

I m trying to create a simple Caesar Cipher function in Python that shifts letters based on input from the user and creates a final  new string at the end  The only problem is that the final cipher text shows only the last shifted character  not an entire string with all the shifted characters    Here s my code   plainText   raw input  What is your plaintext     shift   int raw input  What is your shift       def caesar plainText  shift         for ch in plainText          if ch isalpha                stayInAlphabet   ord ch    shift              if stayInAlphabet  gt  ord  z                    stayInAlphabet -  26             finalLetter   chr stayInAlphabet          cipherText              cipherText    finalLetter      print  Your ciphertext is     cipherText      return cipherText  caesar plainText  shift

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You need to move cipherText      before the start of the for loop   You re resetting it each time through the loop   def caesar plainText  shift      cipherText        for ch in plainText      if ch isalpha          stayInAlphabet   ord ch    shift        if stayInAlphabet  gt  ord  z            stayInAlphabet -  26       finalLetter   chr stayInAlphabet        cipherText    finalLetter   print  Your ciphertext is     cipherText   return cipherText

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This is an improved version of the code in the answer of  amillerrhodes that works with different alphabets  not just lowercase   def caesar text  step  alphabets        def shift alphabet           return alphabet step     alphabet  step       shifted alphabets   tuple map shift  alphabets       joined aphabets      join alphabets      joined shifted alphabets      join shifted alphabets      table   str maketrans joined aphabets  joined shifted alphabets      return text translate table    Example of usage    gt  gt  gt  import string  gt  gt  gt  alphabets    string ascii lowercase  string ascii uppercase  string digits   gt  gt  gt  caesar  Abc-xyZ 012 789         step 4  alphabets alphabets   Efg-bcD 456 123            References  Docs on str maketrans  Docs on str translate  Docs on the string library

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The code is very large  but easy to understand  I think it fits your situation  alphabet    quot abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz quot  class CaesarCipher object           def   init   self  shift           self shift   shift     def encode self  str           encode              str   str lower           for i in str              if i in alphabet                  encode    alphabet alphabet index i    self shift              else                  encode    i              return encode upper         def decode self  str           decode              str   str lower           for i in str              if i in alphabet                  decode    alphabet alphabet index i  - self shift              else                  decode    i         return decode upper

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The problem is that you set cipherText to empty string at every cycle iteration  the line  cipherText        must be moved before the loop

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Batteries included   while 1      phrase   raw input  Could you please give me a phrase to encrypt  n       if phrase         break     print  Here it is your phrase  encrypted       print phrase encode  rot 13   print  Have a nice afternoon     https   docs python org 2 library codecs html python-specific-encodings  Python 3 update  The fine docs say      Now the rot 13  codec provides a text transform  a str to str mapping  It is not supported by str encode    which only produces bytes output     Or  in other words  you have to import encode from the codecs module and use it with the string to be encoded as its first argument  from codecs import decode         print encode phrase   rot13

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message    The quick brown fox jumped over the lazy dog  1234567890        amp      -  encrypted      join chr ord char  3  for char in message  decrypted      join chr ord char -3  for char in encrypted  print encrypted  print decrypted    Wkh txlfn eurzq ir  mxpshg ryhu wkh od   grj1 456789   lt 3  C amp   a -  b 0   The quick brown fox jumped over the lazy dog  1234567890        amp      -

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This solution is more intuitively without the use of ord function  def caesar cipher raw text  key       alphabet    quot ABCDEFGHIJKLMNOPQRSTUVWXYZ quot      shifted alphabet   alphabet 26-key   alphabet 0  26-key       cipher text    quot  quot      for i in range len raw text            char   raw text i          idx   alphabet find char upper            if idx    -1              cipher text   cipher text   char         elif char islower                cipher text   cipher text   shifted alphabet idx  lower           else              cipher text   cipher text   shifted alphabet idx       return cipher text   And an example  plain text    quot The quick brown fox jumps over the lazy dog  quot  caesar cipher plain text 3   And we get   Qeb nrfzh yoltk clu grjmp lsbo qeb ixwv ald    If we want to decrypt it  caesar cipher caesar cipher plain text 3  26-3   and we get   The quick brown fox jumps over the lazy dog    More details here https   predictivehacks com caesar-cipher-in-python

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import string wrd raw input  Enter word   lower   fwrd    for let in wrd      fwrd  string ascii lowercase  string ascii lowercase  index let  3  print Original word  wrd print New word  fwrd

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Here  a more functional way   if you use shift i to encode  then use -i to decode   def ceasar story  shift     return    join     concentrate list to string              lambda c  is upper  c upper   if is upper else c    if original char is upper case than convert result to upper case too                                       abcdefghijklmnopqrstuvwxyz  2  ord char lower    - ord  a     shift   26     rotate char  this is extra easy since Python accepts list indexs below 0                   char isupper                                 if char isalpha   else char   if not in alphabet then don t change it             for char in story

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For example  decod string   quot uo jxuhu  jxyi yi qd unqcfbu ev q squiqh syfxuh  muhu oek qrbu je tusetu yj  y xefu ie  iudt cu q cuiiqwu rqsa myjx jxu iqcu evviuj  quot   This message has an offset of 10  Code below  import string alphabet   list string ascii lowercase  print alphabet  len alphabet   messege    quot xuo jxuhu  jxyi yi qd unqcfbu ev q squiqh syfxuh  muhu oek qrbu je tusetu yj  y xefu ie  iudt cu q cuiiqwu rqsa myjx jxu iqcu evviuj  quot  messege split   messege split   print messege split   encrypted messege    quot  quot  position   0 for i in messege split      for j in i          if ord j   lt  65              encrypted messege    j         else                       for k in alphabet                  if j    k                      position   alphabet index k                      if  position   10   gt   len alphabet                           encrypted messege    alphabet abs  position   10  - len alphabet                        else                          encrypted messege    alphabet position   10      encrypted messege     quot   quot   print encrypted messege   Decoded string   quot hey there  this is an example of a caesar cipher  were you able to decode it  i hope so  send me a message back with the same offset  quot  TRY IT

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def encrypt        plainText   input  What is your plaintext         shift   int input  What is your shift          cipherText          for ch in plainText          if ch isalpha                stayInAlphabet   ord ch    shift         if stayInAlphabet  gt  ord  z                stayInAlphabet -  26         finalLetter   chr stayInAlphabet          cipherText    finalLetter      print   Your ciphertext is     cipherText  with a shift of  shift    def decrypte        encryption input  enter in your encrypted code       encryption shift int input  enter in your encryption shift         cipherText1          for c in encryption          if c isalpha                stayInAlphabet1   ord c  - encryption shift         if stayInAlphabet1  gt  ord  z                stayInAlphabet1    26         finalLetter1   chr stayInAlphabet1          cipherText1    finalLetter1      print   Your ciphertext is     cipherText1  with negative shift of  encryption shift   from tkinter import    menu Tk   menu title  menu   menu geometry  300x300   button1  Button menu text  encrypt  command encrypt  button1 pack    button2  Button menu text  decrypt  command decrypte  button2 pack    button3  Button menu text  exit  command exit  button3 pack    menu mainloop

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plainText   raw input  What is your plaintext     shift   int raw input  What is your shift       def caesar plainText  shift        for ch in plainText          if ch isalpha                stayInAlphabet   ord ch    shift              if stayInAlphabet  gt  ord  z                    stayInAlphabet -  26             finalLetter   chr stayInAlphabet               HERE YOU RESET CIPHERTEXT IN EACH ITERATION              cipherText              cipherText    finalLetter      print  Your ciphertext is     cipherText      return cipherText  caesar plainText  shift    As an else to if ch isalpha   you can put finalLetter ch   You should remove the line  cipherText       Cheers

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As pointed by others  you were resetting the cipherText in the iteration of the for loop  Placing cipherText before the start of the for loop will solve your problem   Additionally  there is an alternate approach to solving this problem using Python s Standard library  The Python Standard Library defines a function maketrans   and a method translate that operates on strings   The function maketrans   creates translation tables that can be used with the translate method to change one set of characters to another more efficiently   Quoted from The Python Standard Library by Example    import string  def caesar plaintext  shift     shift    26   Values greater than 26 will wrap around  alphabet lower   string ascii lowercase alphabet upper   string ascii uppercase  shifted alphabet lower   alphabet lower shift     alphabet lower  shift  shifted alphabet upper   alphabet upper shift     alphabet upper  shift   alphabet   alphabet lower   alphabet upper  shifted alphabet   shifted alphabet lower   shifted alphabet upper  table   string maketrans alphabet  shifted alphabet    return plaintext translate table

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gt  gt  gt  def rotate txt  key         def cipher i  low range 97 123   upper range 65 91            if i in low or i in upper            s   65 if i in upper else 97           i    i - s   key    26   s         return chr i        return    join  cipher ord s   for s in txt      test  gt  gt  gt  rotate  abc   2   cde   gt  gt  gt  rotate  xyz   2   zab   gt  gt  gt  rotate  ab   26   ab   gt  gt  gt  rotate  Hello  World    7   Olssv  Dvysk

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Why not use the function reverse on the shift input  and and join the plain text with the shift  and input it as the cipher text   Plain   int input  enter a number      Rev   plain   -1  Cipher       join for cipher text in Rev

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from string import ascii lowercase as alphabet  class CaesarCypher      alpha len   len alphabet      min guess rate   0 2   Encryption and decryption is a same stuff  when you want to decrypt for example with shift 10 that means that you can encrypt it with shift 26 - 10  In this case cycle will repeat at if you going to shift whole alphabet it will be the same  Also here i ve proceed upper case and non chars      def   call   self  text  offset  encrypt True           if not encrypt              offset   self alpha len - offset         result              for letter in text              if not letter isalpha                    result append letter                  continue             letter to process   letter lower               processed letter   self  encrypt letter letter to process  offset              if letter isupper                    processed letter   processed letter upper               result append processed letter          return    join result    all encryption goes here at most           def  encrypt letter self  letter  offset 0           position    alphabet find letter    offset    self alpha len         return alphabet position    this part is for broot force and guess throug dictionary frequency        staticmethod     def   how many do i know text           clean words   filter lambda x  x isalpha    text split            clean words             format x  for x in clean words          cursor   conn cursor           query    SELECT COUNT    FROM mydictionary WHERE word IN       format     join clean words           cursor execute query          response   cursor fetchone   0          return response   len clean words       def guess encode self  text           options    self text  offset  encrypt False  for offset in range self alpha len           best option    self   how many do i know option  for option in options          best key  guess rate   max enumerate best option   key lambda x  x -1           guess text   options best key          return best key  guess rate  guess text

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Using map  def caesar text  key       return    join map lambda c           chr  ord c lower    - ord  a     key    26   ord  a    if c isalpha   else          text

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according to me this answer is useful for you   def casear a key   str    if key gt 26      key  26 for i in range 0 len a        if a i  isalpha            b ord a i           b  key          if b gt 90                     if upper case letter ppear in your string              c b-90                  if upper case letter ppear in your string              str  chr 64 c           if upper case letter ppear in your string         if b gt 122              c b-122             str  chr 96 c          else              str  chr b      else          str  a i  print str  a raw input   key int input    casear a key    This function shifts all letter to right according to given key

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Using some ascii number tricks     See http   ascii cl  upper    ascii chr ascii  for ascii in range 65 91   lower    ascii chr ascii  for ascii in range 97 123   digit    ascii chr ascii  for ascii in range 48 58     def ceasar s  k       for c in s          o   ord c            Do not change symbols and digits         if  o not in upper and o not in lower  or o in digit              yield o         else                If it s in the upper case and               that the rotation is within the uppercase             if o in upper and o   k   26 in upper                  yield o   k   26               If it s in the lower case and               that the rotation is within the lowercase             elif o in lower and o   k   26 in lower                  yield o   k   26               Otherwise move back 26 spaces after rotation              else    alphabet                  yield o   k   26 -26  x       join map chr  ceasar s  k     print  x

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As  I82much said  you need to take cipherText      outside of your for loop  Place it at the beginning of the function  Also  your program has a bug which will cause it to generate encryption errors when you get capital letters as input  Try       if ch isalpha             finalLetter   chr  ord ch lower    - 97   shift    26   97

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key   3  def wub        def choice            choice   input  Do you wish to Encrypt of Decrypt            choice   choice lower           if choice     e  or  encrypt               return choice         elif choice     d  or  decrypt               return choice         else              print  Invalid response  please try again                choice        def message            user   input  Enter your message             return user      def waffle choice  message  key           translated              if choice     e  or  encrypt               for character in message                  num   ord character                  num    key                 translated    chr num                   derek   open  Encrypted txt    w                   derek write translated              derek close               return translated         else              for character in message                  num   ord character                  num -  key                 translated    chr num              return translated      choice   choice    Runs function for encrypt decrypt selection  Saves choice made      message   message    Run function for user to enter message  Saves message      final   waffle choice  message  key   Runs function to translate message  using the choice  message and key variables      print   n Operation complete        print final   wub

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I realize that this answer doesn t really answer your question  but I think it s helpful anyway  Here s an alternative way to implementing the caesar cipher with string methods   def caesar plaintext  shift       alphabet   string ascii lowercase     shifted alphabet   alphabet shift     alphabet  shift      table   string maketrans alphabet  shifted alphabet      return plaintext translate table    In fact  since string methods are implemented in C  we will see an increase in performance with this version  This is what I would consider the  pythonic  way of doing this

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caesar-cipher message   str input  quot Enter you message  quot    shift   int input  quot Enter a number  quot      encode  stringValue    ord message  - 96 for message in message  print stringValue  encode msg val         encode msg val append int stringValue i   shift  for i in  range len stringValue     encode msg array      for i in range len encode msg val        encode val   encode msg val i    96     encode msg array append chr encode val    print encode msg array  encode msg      join encode msg array      dedcode   deocde msg val    ord encode msg  - 96 for encode msg in encode msg   decode val       decode val append deocde msg val i  - shift  for i in  range len deocde msg val     decode msg array       decode msg array append decode val i    96  for i in range len decode val     decode msg list       decode msg list append chr decode msg array i    for i in  range len decode msg array     decode msg      join decode msg list  print decode msg

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Using cyclic generator  import string from itertools import cycle   def caesarCipherEncryptor s  key       def generate letters            yield from cycle string ascii lowercase           def find next v  g  c             Eat up characters until we arrive at the plaintext character         while True              if v    next g                   break                    Increment the plaintext character by the count using the generator         try              for   in range c                   item   next g              return item         except UnboundLocalError              return v      return  quot  quot  join  find next i  generate letters    key  for i in s      Outputs  gt  gt  gt  caesarCipherEncryptor  quot xyz quot   3   gt  gt  gt   abc

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I have a hard time remember the char to int conversions so this could be optimized  def decryptCaesar encrypted  shift       minRange   ord  a       decrypted          for char in encrypted          decrypted    chr   ord char  - minRange   shift    26    minRange       return decrypted

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def encrypt text shift               INPUT  text as a string and an integer for the shift value      OUTPUT  The shifted text after being run through the Caeser cipher                 Create a placeholder list     encrypted text   list range len text         alphabet   string ascii lowercase        Create shifted alphabet     first half   alphabet  shift      second half   alphabet shift       shifted alphabet   second half first half      for i letter in enumerate text lower                Check for spaces or punctuation         if letter in alphabet                Find the original index position             original index   alphabet index letter                 Shifted letter             new letter   shifted alphabet original index               encrypted text i    new letter            Punctuation or space         else              encrypted text i    letter      return    join encrypted text

[python] Caesar Cipher Function in Python

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