Python split string in moving window

Question

I have a string with digits like so - digit = "7316717"

Now I want to split the string in such a way that the output is a moving window of 3 digits at a time. So I get -

["731", "316", "167", "671", "717"]

How would the approach be? Straightforward way is to put in for-loop and iterate. But I feel some inbuilt python string function can do this in less code. Know of any such approach?

Answer 1

The itertools examples provides the window function that does just that:

from itertools import islice
def window(seq, n=2):
    "Returns a sliding window (of width n) over data from the iterable"
    "   s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ...                   "
    it = iter(seq)
    result = tuple(islice(it, n))
    if len(result) == n:
        yield result    
    for elem in it:
        result = result[1:] + (elem,)
        yield result

Example usage:

>>> ["".join(x) for x in window("7316717", 3)]
['731', '316', '167', '671', '717']

Answer 2

>>> s = "7316717"
>>> [s[i:i+3] for i in range(len(s)-2)]
['731', '316', '167', '671', '717']

Answer 3

There is a very good recipe pairwise in itertools docs.

Modernizing it a bit for n elements in the group, I made this code:

from itertools import tee, izip

def window(iterable, n):
    els = tee(iterable, n)
    for i, el in enumerate(els):
        for _ in xrange(i):
            next(el, None)
    return izip(*els)


print(["".join(i) for i in window("2316515618", 3)])

Python 2.7