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When is it appropriate to use dict.items() vs dict.iteritems. Both
seem to work for something like:

for key,val in mydict.items():
print key,val

for key,val in mydict.iteritems():
print key,val

Also, when is it appropriate to use range() vs xrange(). From my
understanding, xrange() essentially gives you an iterator across a
range, so it should be used when iterating. Should you only use
range() when want to physically store the range as a list?

Thanks,
Drew

Drew a écrit :
> When is it appropriate to use dict.items() vs dict.iteritems. Both
> seem to work for something like:
>
> for key,val in mydict.items():
> print key,val
>
> for key,val in mydict.iteritems():
> print key,val
>
> Also, when is it appropriate to use range() vs xrange(). From my
> understanding, xrange() essentially gives you an iterator across a
> range, so it should be used when iterating. Should you only use
> range() when want to physically store the range as a list?

iteritems and xrange only provide values when requested.
items and range build complete list when called.

Both work, you may prefer xrange/iteritems for iteration on large
collections, you may prefer range/items when processing of the result
value explicitly need a list (ex. calculate its length) or when you are
going to manipulate the original container in the loop.

A+

Laurent.

On Mar 14, 11:44 am, Laurent Pointal <laurent.poin...@limsi.fr> wrote:
> Both work, you may prefer xrange/iteritems for iteration on large
> collections, you may prefer range/items when processing of the result
> value explicitly need a list (ex. calculate its length) or when you are
> going to manipulate the original container in the loop.
>
> A+
>
> Laurent.

Laurent -

Extremely helpful, exactly what I was looking for.

Thanks,
Drew

# Just by looking at the output, it seems pretty obvious that xrange
would be more memory effcient for large ranges:

print "With range():",range(100,200)
print
print "With xrange():",xrange(100,200)

d = {1:2,2:3,3:4}
d.items()
d.iteritems()

# I have been curious to use Pysizer (which requires patching Python)
to demonstrate the difference.



Drew wrote:
> When is it appropriate to use dict.items() vs dict.iteritems. Both
> seem to work for something like:
>
> for key,val in mydict.items():
> print key,val
>
> for key,val in mydict.iteritems():
> print key,val
>
> Also, when is it appropriate to use range() vs xrange(). From my
> understanding, xrange() essentially gives you an iterator across a
> range, so it should be used when iterating. Should you only use
> range() when want to physically store the range as a list?
>
> Thanks,
> Drew
>
>

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IT Director
National Council on Economic Education
| 402-438-8958 | http://www.ncee.net

Leading the Campaign for Economic and Financial Literacy

Laurent Pointal wrote:
> Both work, you may prefer xrange/iteritems for iteration on large
> collections, you may prefer range/items when processing of the result
> value explicitly need a list (ex. calculate its length) or when you are
> going to manipulate the original container in the loop.

xrange actually supports len():

>>> len(xrange(10))
10

>> When is it appropriate to use dict.items() vs dict.iteritems.

Laurent> Both work, you may prefer xrange/iteritems for iteration on
Laurent> large collections...

I find "iter<anything>" to be extremely ugly and hope to avoid using them
altogether until they are gone in Py3k.

Skip

On Mar 14, 2:53 pm, s...@pobox.com wrote:
> >> When is it appropriate to use dict.items() vs dict.iteritems.
>
> Laurent> Both work, you may prefer xrange/iteritems for iteration on
> Laurent> large collections...
>
> I find "iter<anything>" to be extremely ugly and hope to avoid using them
> altogether until they are gone in Py3k.
>
> Skip

Skip -

Ugly, maybe, but don't you take a decent performance hit when loading
the entire dict into memory at once? Especially if the dict is large?

>> I find "iter<anything>" to be extremely ugly and hope to avoid using
>> them altogether until they are gone in Py3k.

Drew> Ugly, maybe, but don't you take a decent performance hit when
Drew> loading the entire dict into memory at once? Especially if the
Drew> dict is large?

Sure, but I try hard to keep my dicts small.

Skip

Laurent Pointal <> writes:
> Both work, you may prefer xrange/iteritems for iteration on large
> collections, you may prefer range/items when processing of the result
> value explicitly need a list (ex. calculate its length) or when you are
> going to manipulate the original container in the loop.

You can use len(d) if d is a dict.

Paul Rubin a écrit :
> Laurent Pointal <> writes:
>> Both work, you may prefer xrange/iteritems for iteration on large
>> collections, you may prefer range/items when processing of the result
>> value explicitly need a list (ex. calculate its length) or when you are
>> going to manipulate the original container in the loop.
>
> You can use len(d) if d is a dict.

Yes, as long as you have a semantic relation between the original dict
and the extracted keys. But once you have extracted the keys, and pass
them around your functions, if you miss the relationship, you have
either a list container or a generator. Not considering the case where
original dict is modified between keys extraction and keys usage...

But as we dont know more about OP needs...


A+

Laurent.