Dave Angel <davea <at> davea.name> writes:
>
> > str_num = '1234567890'
> > n = 5
> >
> > strings = [str_num[i:i+5] for i in range(0, len(str_num)) if
> > len(str_num[i:i+5])==5]
>
> If you changed the range() size, you could eliminate the extra if test.
> After all, the only ones that'll be short are the last 4. Also,
> xrange is better than range, if you ever try this on a really big
> dataset. Good habit to get into, and in Python 3.x, the original range
> is gone, and xrange is called range.
>
> strings = [str_num[i:i+5] for i in xrange(0, len(str_num-4)) ]
>
Of course, if you're really concerned about the size of your dataset, then
you should combine xrange (or range in Python 3) with a generator expression
instead of a list comprehension to yield substrings only one at a time.
This is very easy to do: just replace your square brackets with parentheses:
strings = (str_num[i:i+5] for i in xrange(0, len(str_num-4)))
Since this is in expression you might find useful again for other tasks, you
could encapsulate it in a (very short) function:
def slider (s, window):
return (s[i:i+window] for i in range(0, len(s)-window+1))
that you can use conveniently in a for loop:
for substr in slider(str_num, 5):
or in a comprehension, like:
products = [product(substr) for substr in slider(str_num, 5)]
for your code.
Best,
Wolfgang
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
