Iterate over a string 2 (or n) characters at a time in Python

>>> s = "+c-R+D-e"
>>> s
'+c-R+D-e'
>>> s[::2]
'+-+-'
>>>

Maybe this would be cleaner?

s = "+c-R+D-e"
for i in xrange(0, len(s), 2):
    op, code = s[i:i+2]
    print op, code

You could perhaps write a generator to do what you want, maybe that would be more pythonic 🙂

from itertools import izip_longest
def grouper(iterable, n, fillvalue=None):
    args = [iter(iterable)] * n
    return izip_longest(*args, fillvalue=fillvalue)
def main():
    s = "+c-R+D-e"
    for item in grouper(s, 2):
        print ' '.join(item)
if __name__ == "__main__":
    main()
##output
##+ c
##- R
##+ D
##- e

izip_longest requires Python 2.6( or higher). If on Python 2.4 or 2.5, use the definition for izip_longest from the document or change the grouper function to:

from itertools import izip, chain, repeat
def grouper(iterable, n, padvalue=None):
    return izip(*[chain(iterable, repeat(padvalue, n-1))]*n)

The other answers work well for n = 2, but for the general case you could try this:

def slicen(s, n, truncate=False):
    nslices = len(s) / n
    if not truncate and (len(s) % n):
        nslices += 1
    return (s[i*n:n*(i+1)] for i in range(nslices))

>>> s = '+c-R+D-e'
>>> for op, code in slicen(s, 2):
...     print op, code
... 
+ c
- R
+ D
- e

>>> for a, b, c in slicen(s, 3):
...     print a, b, c
... 
+ c -
R + D
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: need more than 2 values to unpack

>>> for a, b, c in slicen(s,3,True):
...     print a, b, c
... 
+ c -
R + D

Great opportunity for a generator. For larger lists, this will be much more efficient than zipping every other elemnent. Note that this version also handles strings with dangling ops

def opcodes(s):
    while True:
        try:
            op   = s[0]
            code = s[1]
            s    = s[2:]
        except IndexError:
            return
        yield op,code        


for op,code in opcodes("+c-R+D-e"):
   print op,code

edit: minor rewrite to avoid ValueError exceptions.

Triptych inspired this more general solution:

def slicen(s, n, truncate=False):
    assert n > 0
    while len(s) >= n:
        yield s[:n]
        s = s[n:]
    if len(s) and not truncate:
        yield s

for op, code in slicen("+c-R+D-e", 2):
    print op,code

Maybe not the most efficient, but if you like regexes…

import re
s = "+c-R+D-e"
for op, code in re.findall('(.)(.)', s):
    print op, code

This approach support an arbitrary number of elements per result, evaluates lazily, and the input iterable can be a generator (no indexing is attempted):

import itertools

def groups_of_n(n, iterable):
    c = itertools.count()
    for _, gen in itertools.groupby(iterable, lambda x: c.next() / n):
        yield gen

Any left-over elements are returned in a shorter list.

Example usage:

for g in groups_of_n(4, xrange(21)):
    print list(g)

[0, 1, 2, 3]
[4, 5, 6, 7]
[8, 9, 10, 11]
[12, 13, 14, 15]
[16, 17, 18, 19]
[20]

I ran into a similar problem. Ended doing something like this:

ops = iter("+c-R+D-e")
for op in ops
    code = ops.next()

    print op, code

I felt it was the most readable.

Here’s my answer, a little bit cleaner to my eyes:

for i in range(0, len(string) - 1):
    if i % 2 == 0:
        print string[i:i+2]

Consider pip installing more_itertools, which already ships with a chunked implementation along with other helpful tools:

import more_itertools 

for op, code in more_itertools.chunked(s, 2):
    print(op, code)

Output:

+ c
- R
+ D
- e

I made this simple generator:

def every_two(s):
    d = list(s)
    c = True
    for i in range(len(d)):
        if c:
            c = False
            yield d[i], d[i+1]
        else:
            c = True

It will raise an IndexError if the lenght of the string isn’t divisible by two but you can just wrap the yield statement in a try block.