How to iterate over a string using a buffer (python)

Question

Hi all,

I'm trying to find some code that, given a string, will allow me to iterate over each line using the for loop construct, but with the added requirement that separate for loop constructs will not reset the iteration back to the beginning.

At the moment I have

sList = [line for line in theString.split(os.linesep)]
for line in SList
  ... do stuff

But successive for loops will reset the iteration back to the beginning.

Does something in python exist for this, or will I have to write one from scratch?

Thanks

Tarsa

Answer 1

Try using a combination of slices and enumerate():

sList = theString.split(os.linesep)
for i, line in enumerate(sList):
    if foo: 
        break

for j, line in enumerate(sList[i:]):
    # do more stuff

Answer 2

Just use a generator expression (genexp) instead of the list comprehension (listcomp) you're now using - i.e.:

sList = (line for line in theString.split(os.linesep))

that's all -- if you're otherwise happy with your code (splitting by os.linesep, even though normal text I/O in Python will already have translated those into \n...), all you need to do is to use parentheses (the round kind) instead of brackets (the square kind), and you'll get a generator instead of a list.

Now, each time you do a for line in sList:, it will start again from where the previous one had stopped (presumably because of a break) -- that's what you're asking for, right?

Answer 3

Hack at an iterator?

def iterOverList(someList):
    for i in someList:
        # Do some stuff
        yield

Then just call iterOverList() within a loop a few times, it'll retain state?

Answer 4

Use another iterator:

aList = range(10)
anIterator = iter(aList)

for item in anIterator:
    print item
    if item > 4: break

for item in anIterator:
    print item