What is the simplest way to swap each pair of adjoining chars in a string with Python

Question

I want to swap each pair of characters in a string   2143  becomes  1234    badcfe  becomes  abcdef    How can I do this in Python

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A bit late to the party  but there is actually a pretty simple way to do this   The index sequence you are looking for can be expressed as the sum of two sequences    0  1  2  3      1 -1  1 -1       Both are easy to express  The first one is just range N   A sequence that toggles for each i in that range is i   2  You can adjust the toggle by scaling and offsetting it            i   2      - gt   0  1  0  1          1 - i   2      - gt   1  0  1  0     2    1 - i   2      - gt   2  0  2  0     2    1 - i   2  - 1 - gt   1 -1  1 -1       The entire expression simplifies to i   1 - 2    i   2   which you can use to join the string almost directly   result      join string i   1 - 2    i   2   for i in range len string      This will work only for an even-length string  so you can check for overruns using min   N   len string  result      join string min i   1 - 2    i   2   N - 1   for i in range N     Basically a one-liner  doesn t require any iterators beyond a range over the indices  and some very simple integer math

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One more way    gt  gt  gt  s  123456   gt  gt  gt     join     join el  for el in zip s 1  2   s 0  2      214365

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re sub r         r  2 1   abcdef1234     However re is a bit slow   def swap s       i iter s      while True          a b next i  next i          yield b         yield a     join swap  abcdef1234

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Loop over length of string by twos and swap   def oddswap st       s   list st      for c in range 0 len s  2           t s c          s c  s c 1          s c 1  t      return    join s    giving    gt  gt  gt  s  foobar   gt  gt  gt  oddswap s   ofbora    and fails on odd-length strings with an IndexError exception

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Works on even odd size strings str    2143657  newStr      for i in range len str   2       newStr    str i 2 1    str i 2  if len str  2    0      newStr    str -1  print newStr

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A more general answer    you can do any single pairwise swap with tuples or strings using this approach     item can be a string or tuple and swap can be a list or tuple of two   indices to swap def swap items by copy item  swap      s0   min swap     s1   max swap     if isinstance item str           return item  s0  item s1  item s0 1 s1  item s0  item s1 1      elif isinstance item tuple           return item  s0   item s1    item s0 1 s1   item s0    item s1 1      else          raise ValueError  Type not supported     Then you can invoke it like this    gt  gt  gt  swap items by copy  1 2 3 4 5 6   1 2    1  3  2  4  5  6   gt  gt  gt  swap items by copy  hello   1 2    hlelo   gt  gt  gt     Thankfully python gives empty strings or tuples for the cases where the indices refer to non existent slices

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gt  gt  gt  import ctypes  gt  gt  gt  s    abcdef   gt  gt  gt  mutable   ctypes create string buffer s   gt  gt  gt  for i in range 0 len s  2    gt  gt  gt      mutable i   mutable i 1    mutable i 1   mutable i   gt  gt  gt  s   mutable value  gt  gt  gt  print s badcfe

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Like so    gt  gt  gt  s    2143658709   gt  gt  gt     join  s i 1    s i  for i in range 0  len s   2     1234567890    gt  gt  gt  s    badcfe   gt  gt  gt     join  s i 1    s i  for i in range 0  len s   2     abcdef

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Do you want the digits sorted  Or are you swapping odd even indexed digits   Your example is totally unclear    Sort   s    2143  p list s  p sort   s      join p    s is now  1234   The trick is here that list string  breaks it into characters

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If performance or elegance is not an issue  and you just want clarity and have the job done then simply use this   def swap text  ch1  ch2       text   text replace ch2            text   text replace ch1  ch2      text   text replace      ch1      return text   This allows you to swap or simply replace chars or substring  For example  to swap  ab   lt -   de  in a text    str    abcdefabcdefabcdef  print swap  str   ab   de    decabfdecabfdecabf

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Think about how index works with string in Python   gt  gt  gt  a    123456   gt  gt  gt  a   -1   654321

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While the above solutions do work  there is a very simple solution shall we say in  quot layman s quot  terms  Someone still learning python and string s can use the other answers but they don t really understand how they work or what each part of the code is doing without a full explanation by the poster as opposed to  quot this works quot   The following executes the swapping of every second character in a string and is easy for beginners to understand how it works  It is simply iterating through the string  any length  by two s  starting from 0 and finding every second character  and then creating a new string  swapped pair  by adding the current index   1  second character  and then the actual index  first character   e g   index 1 is put at index 0 and then index 0 is put at index 1 and this repeats through iteration of string  Also added code to ensure string is of even length as it only works for even length  DrSanjay Bhakkad post above is also a good one that works for even or odd strings and is basically doing the same function as below  string    quot abcdefghijklmnopqrstuvwxyz123 quot     use this prior to below iteration if string needs to be even but is possibly odd if len string    2    0      string   string  -1     iteration to swap every second character in string swapped pair    quot  quot  for i in range 0  len string   2       swapped pair     string i   1    string i      use this after above iteration for any even or odd length of strings if len swapped pair    2    0      swapped adj    swapped pair -1   print swapped pair   badcfehgjilknmporqtsvuxwzy21   output if the  quot needs to be even quot  code used badcfehgjilknmporqtsvuxwzy213   output if the  quot even or odd quot  code used

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join s i 1  s i  for i in range 0  len s   2     10 6 usec per loop   or     join x y for x  y in zip s 1  2   s   2      10 3 usec per loop   or if the string can have an odd length      join x y for x  y in itertools izip longest s 1  2   s   2   fillvalue        Note that this won t work with old versions of Python  if I m not mistaking older than 2 5    The benchmark was run on python-2 7-8 fc14 1 x86 64 and a Core 2 Duo 6400 CPU with s  0123456789  4

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To swap characters in a string a of position l and r def swap a  l  r       a   a 0 l    a r    a l 1 r    a l    a r 1       return a  Example  swap  quot aaabcccdeee quot   3  7  returns  quot aaadcccbeee quot

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The usual way to swap two items in Python is   a  b   b  a   So it would seem to me that you would just do the same with an extended slice  However  it is slightly complicated because strings aren t mutable  so you have to convert to a list and then back to a string  Therefore  I would do the following    gt  gt  gt  s    badcfe   gt  gt  gt  t   list s   gt  gt  gt  t   2   t 1  2    t 1  2   t   2   gt  gt  gt     join t   abcdef

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Here s one way      gt  gt  gt  s    2134   gt  gt  gt  def swap c  i  j        c   list c       c i   c j    c j   c i       return    join c       gt  gt  gt  swap s  0  1   1234   gt  gt  gt

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There is no need to make a list  The following works for even-length strings   r      for in in range 0  len s   2      r    s i   1    s i  s   r

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def revstr a       b        if len a  2  0          for i in range 0 len a  2               b    a i   1    a i          a b     else          c a -1          for i in range 0 len a -1 2               b    a i   1    a i          b b a -1          a b     return b a raw input  enter a string   n revstr a  print n

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oneliner    gt  gt  gt  s    badcfe   gt  gt  gt     join   s x x 2    -1  for x in range 0  len s   2      abcdef     s x x 2  returns string slice from x to x 2  it is safe for odd len s      -1  reverses the string in Python range 0  len s   2  returns 0  2  4  6     while x  lt  len s

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One of the easiest way to swap first two characters from a String is inputString    2134   extractChar   inputString 0 2  swapExtractedChar   extractChar   -1            quot  quot  quot Reverse the order of string quot  quot  quot  swapFirstTwoChar   swapExtractedChar   inputString 2       swapFirstTwoChar   inputString 0 2    -1    inputString 2        quot  quot  quot For one line code quot  quot  quot   print swapFirstTwoChar

[python] What is the simplest way to swap each pair of adjoining chars in a string with Python?

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