[Python-ideas] Consider making enumerate a sequence if its argument is a sequence
mistersheik at gmail.com
Wed Sep 30 20:46:04 CEST 2015
It doesn't behave like a generator because it doesn't implement send,
throw, or close. It's a sequence because it implements: __getitem__,
__len__ __contains__, __iter__, __reversed__, index, and count.
On Wed, Sep 30, 2015 at 2:43 PM M.-A. Lemburg <mal at egenix.com> wrote:
> On 30.09.2015 20:26, Andrew Barnert via Python-ideas wrote:
> > On Sep 30, 2015, at 11:11, M.-A. Lemburg <mal at egenix.com> wrote:
> >>> On 30.09.2015 19:19, Neil Girdhar wrote:
> >>> I guess, I'm just asking for enumerate to go through the same change
> >>> range went through. Why wasn't it a problem for range?
> >> range() returns a list in Python 2 and a generator in Python 3.
> > No it doesn't. It returns a (lazy) sequence. Not a generator, or any
> other kind of iterator.
> You are right that it's not of a generator type
> and more like a lazy sequence. To be exact, it returns
> a range object and does implement the iter protocol via
> a range_iterator object.
> In Python 2 we have the xrange object which has similar
> properties, but not the same, e.g. you can't slice it.
> > I don't know why so many people seem to believe it returns a generator.
> (And, when you point out what it returns, most of them say, "Why was that
> changed from 2.x xrange, which returned a generator?" but xrange never
> returned a generator either--it returned a lazy almost-a-sequence from the
> Perhaps because it behaves like one ? :-)
> Unlike an iterator, it doesn't iterate over a sequence, but instead
> generates the values on the fly.
> FWIW: I don't think many people use the lazy sequence features
> of range(), e.g. the slicing or index support. By far most
> uses are in for-loops.
> Marc-Andre Lemburg
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