Getting two characters from string in python

You can use slice notation. long_str[x:y] will give you characters in the range [x, y) (where x is included and y is not).

>>> for i in range(0, len(long_str) - 1, 2):
...   print long_str[i:i+2]
... 
ab
cd

Here I am using the three-argument range operator to denote start, end, and step (see http://docs.python.org/library/functions.html).

Note that for a string of odd length, this will not take the last character. If you want the last character by itself, change the second argument of range to len(long_str).

for i, j in zip(long_str[::2], long_str[1::2]):
  print (i+j)

or

import operator
for s in map(operator.add, long_str[::2], long_str[1::2]):
   print (s)

---

itertools also provide a generalized implementation of this:

def grouper(n, iterable, fillvalue=None):
    "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return izip_longest(fillvalue=fillvalue, *args)