how to split a string (or sequence) into pairs of characters?

Brian McErlean b_mcerlean at
Fri Aug 16 18:30:29 CEST 2002

"Jason R. Coombs" <jaraco at> wrote in message news:<ajgp2v$67c$1 at>...
> I have a segment of code that seems particularly ugly.  I want to take a
> sequence and divide it into pairs such that pairs( 'aabbccdd' ) == (
> 'aa','bb','cc','dd' ). Here's code that does what I want.
>   even = range( 0, len( s ), 2 )
>   odd = range( 1, len( s ), 2 )
>   even = map( s.__getitem__, even )
>   odd = map( s.__getitem__, odd )
>   pairs = map( operator.add, even, odd )
> I'd like it to be more elegant and more efficient, and I'd like to avoid
> using loops.  I could obviously do:
>   pairs = []
>   for i in range( 0,len(s),2 ):
>     pairs.append( s[i:i+2] )
> But even that seems a bit inefficient, and doesn't take advantages of the
> powerful sequence operations of Python.
> Can anyone come up with a better way of performing these operations? Extra
> kudos if it easily extends to any sublength and not just pairs.
> Jason

I posted this earlier for a similar request:

class Group:
  def __init__(self, l, size):
    self.l = l

  def __getitem__(self, group):
    idx = group * self.size
    if idx > len(self.l): 
      raise IndexError("Out of range")
    return self.l[idx:idx+self.size]

for pair in Group('aabbccddee',2):
  # do something with pair.

This works with any sequence type (lists, tuples strings etc), lazy,
can be used for any size and should work on any python version from
1.5.2 on.


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