On 02/06/13 15:14, Jim Mooney wrote:
On 1 June 2013 21:20, Steven D'Aprano <st...@pearwood.info> wrote:
On 02/06/13 13:58, Jim Mooney wrote:
It's a little unclear to me where generators are more efficient.
When there are a lot of items, and you access the items one at a time, not
all at once. If there are only a few items, a list or tuple has less
overhead and is easier to use.
So how does one access a generator one element at a time? I thought
next would do that so I tried:
print(next(uneven_squares(10,1000)))
print(next(uneven_squares(10,1000)))
print(next(uneven_squares(10,1000)))
But I got the same answer every time.
That's because you create three independent generators, one after another.
it = uneven_squares(10,1000) # "it" for "iterator"
print(next(it))
print(next(it))
print(next(it))
You can also use the itertools module to slice a generator:
list(itertools.islice(it, 5, 10, 2))
This call to islice will grab the 5th, 7th and 9th items from it, *starting at
the current position*, and return an iterator. The call to list() converts that
iterator to a list, so you can easily inspect the values. Here's an example:
py> it = iter("abcdefghijklmnopqrstuvwxyz")
py> next(it)
'a'
py> next(it)
'b'
py> list(itertools.islice(it, 5, 10, 2))
['h', 'j', 'l']
py> next(it)
'm'
--
Steven
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