Insert a newline character every 64 characters using Python

Question

Using Python I need to insert a newline character into a string every 64 characters. In Perl it\'s easy:

s/(.{64})/$1\\n/

How could this be

Answer 1

I suggest the following method:

"\n".join(re.findall("(?s).{,64}", s))[:-1]

This is, more-or-less, the non-RE method taking advantage of the RE engine for the loop.

On a very slow computer I have as a home server, this gives:

$ python -m timeit -s 's="0123456789"*100; import re' '"\n".join(re.findall("(?s).{,64}", s))[:-1]'
10000 loops, best of 3: 130 usec per loop

AndiDog's method:

$ python -m timeit -s "s='0123456789'*100; import re" 're.sub("(?s)(.{64})", r"\1\n", s)'
1000 loops, best of 3: 800 usec per loop

gurney alex's 2nd/Michael's method:

$ python -m timeit -s "s='0123456789'*100" '"\n".join(s[i:i+64] for i in xrange(0, len(s), 64))'
10000 loops, best of 3: 148 usec per loop

I don't consider the textwrap method to be correct for the specification of the question, so I won't time it.

EDIT

Changed answer because it was incorrect (shame on me!)

EDIT 2

Just for the fun of it, the RE-free method using itertools. It rates third in speed, and it's not Pythonic (too lispy):

"\n".join(
   it.imap(
     s.__getitem__,
     it.imap(
       slice,
       xrange(0, len(s), 64),
       xrange(64, len(s)+1, 64)
     )
   )
 )

$ python -m timeit -s 's="0123456789"*100; import itertools as it' '"\n".join(it.imap(s.__getitem__, it.imap(slice, xrange(0, len(s), 64), xrange(64, len(s)+1, 64))))'
10000 loops, best of 3: 182 usec per loop