Splitting a string every 'n'

[Brian McErlean]

Simon.Foster at smiths-aerospace.com wrote in message news:<mailman.1026219434.22644.python-list at python.org>...
> What is the idiomatic way to split a string into a list
> containing 'n' character substrings?  I normally do
> something like:
> 
> while strng:
>     substring = strng[:n]
>     strng = strng[n:]
>     <process substring>
> 
> But the performance of this is hopeless for very long strings!
> Presumable because there's too much list reallocation?  Can't Python
> just optimise this by shuffling the start of the list forward?
> 
> Any better ideas, short of manually indexing through?  Is there
> something like:
> 
> for substring in strng.nsplit():
>     <process substring>

I have a handy class I use for things like this:


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

I use it mainly for grouping things like:
for x,y in Group([1,2,3,4,5,6,7,8,...],2): 
  process_coords(x,y)
but its also applicable to your problem, and works neatly with
strings.

try:

for substring in Group(string, n):
  <process substring>

Don't you just love python's polymorphism!

You don't state what you want to do if the string isn't a multiple of
N characters.  This version includes the shorter string at the end.

Brian.