Generate a list of strings with a sliding window using itertools, yield, and iter() in Python 2.7.1?

Question

I'm trying to generate a sliding window function in Python. I figured out how to do it but not all inside the function. itertools, yield, and iter() are entirely new to me.

i want to input

a='abcdefg'
b=window(a,3)
print b
['abc','bcd','cde','def','efg']

the way i got it work was

def window(fseq, window_size=5):
    import itertools
    tentative=[]
    final=[]
    iteration=iter(fseq)
    value=tuple(itertools.islice(iteration,window_size))
    if len(value) == window_size:
        yield value
    for element in iteration:
        value = value[1:] + (element,)
        yield value

a='abcdefg'
result=window(a)
list1=[]
for k in result:
    list1.append(k)
list2=[]   
for j in list1:
    tentative=''.join(j)
    list2.append(tentative)
print list2

basically what im confused about is how to use the final value of the function inside the function?

here is my code for the function

def window(fseq, window_size=5):
    import itertools
    tentative=[]
    final=[]
    iteration=iter(fseq)
    value=tuple(itertools.islice(iteration,window_size))
    if len(value) == window_size:
        yield value
    for element in iteration:
        value = value[1:] + (element,)
        yield value
    for k in value:
        tentative.append(k)
    for j in tentative:
        tentative_string=''.join(j)
        final.append(tentative_string)
    return final



seq='abcdefg'
uence=window(seq)
print uence

i want it to return the joined list but when i press run it, it says "There's an error in your program * 'return' with argument inside generator"

I'm really confused . . .

possible duplicate of [Python split string in moving window](http://stackoverflow.com/questions/7636004/python-split-string-in-moving-window) — Jon-Eric, Dec 07 '11 at 00:12
Dude... are you going to post the same question every 8 hours? :o — mac, Dec 07 '11 at 08:40
It would still have been wrong: if you ask a question and you don't get answers chances are: (1) you formulated it poorly [ → edit it ] - (2) it's a difficult question [ → answer yourself some question, get reputation points and place a bounty on it ]. Reposting to gain attention is not a welcome behaviour on SO (although I am positive you did not do it with the intention of doing any harm!) :) — mac, Dec 07 '11 at 10:12

Cédric Julien · Accepted Answer · 2011-12-07T08:45:14.873

17

You mean you want to do this ? :

a='abcdefg'
b = [a[i:i+3] for i in xrange(len(a)-2)]
print b
['abc', 'bcd', 'cde', 'def', 'efg']

edited Dec 07 '11 at 08:45

answered Dec 07 '11 at 08:39

Cédric Julien

78,516
15
127
132

2

Shall we use range instead of xrange for more compatibility with python 3 ? – Clement H. Jun 18 '19 at 09:25
@ClementH. original OP was about a python2.7 installation, so, in this case, `xrange` was the best (for memory consumption). Yet, in python3, `range` would be the best solution. If you don't have too big number to iterate on, keep `range` everywhere, otherwise, use [six](https://pypi.org/project/six/). – Cédric Julien Jun 18 '19 at 10:10

score 6 · Answer 2 · answered Dec 07 '11 at 08:41

6

Your generator could be much shorter:

def window(fseq, window_size=5):
    for i in xrange(len(fseq) - window_size + 1):
        yield fseq[i:i+window_size]


for seq in window('abcdefghij', 3):
    print seq


abc
bcd
cde
def
efg
fgh
ghi
hij

answered Dec 07 '11 at 08:41

eumiro

207,213
34
299
261

this is definitely the better option. i didn't know what generators were at the time and didnt have to deal with large datasets like i do now – O.rka Apr 14 '16 at 14:45
In python3, `xrange` is now just `range` – neuron Dec 01 '21 at 16:05

risent · Answer 3 · 2011-12-07T09:24:32.993

2

Use zip function in one line code:

  [ "".join(j) for j in zip(*[fseq[i:] for i in range(window_size)])]

edited Dec 07 '11 at 09:24

answered Dec 07 '11 at 09:19

risent

136
1
4

score 1 · Answer 4 · answered Dec 07 '11 at 08:39

1

def window(fseq,fn):
    alpha=[fseq[i:i+fn] for i in range(len(fseq)-(fn-1))]
    return alpha

answered Dec 07 '11 at 08:39

O.rka

29,847
68
194
309

score 0 · Answer 5 · answered Apr 02 '14 at 11:29

0

>>>def window(data, win_size):
...    tmp = [iter(data[i:]) for i in range(win_size)]
...    return zip(*tmp)
>>> a = [1, 2, 3, 4, 5, 6]
>>> window(a, 3)
>>>[(1,2,3), (2,3,4), (3,4,5), (4,5,6)]

answered Apr 02 '14 at 11:29

Mass Zhou

349
3
6

score 0 · Answer 6 · answered Dec 07 '11 at 08:39

I don't know what your input or expected output are, but you cannot mix yield and return in one function. change return to yield and your function will not throw that error again.

def window(fseq, window_size=5):
    ....
        final.append(tentative_string)
    yield final

Generate a list of strings with a sliding window using itertools, yield, and iter() in Python 2.7.1?

6 Answers6

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