Should you always favor xrange() over range()?

Question

Why or why not?

Answer 1

xrange() is more efficient because instead of generating a list of objects, it just generates one object at a time. Instead of 100 integers, and all of their overhead, and the list to put them in, you just have one integer at a time. Faster generation, better memory use, more efficient code.

Unless I specifically need a list for something, I always favor xrange()

Answer 2

You should favour range() over xrange() only when you need an actual list. For instance, when you want to modify the list returned by range(), or when you wish to slice it. For iteration or even just normal indexing, xrange() will work fine (and usually much more efficiently). There is a point where range() is a bit faster than xrange() for very small lists, but depending on your hardware and various other details, the break-even can be at a result of length 1 or 2; not something to worry about. Prefer xrange().

Answer 3

Go with range for these reasons:

1) xrange will be going away in newer Python versions. This gives you easy future compatibility.

2) range will take on the efficiencies associated with xrange.

Answer 4

For performance, especially when you're iterating over a large range, xrange() is usually better. However, there are still a few cases why you might prefer range():

• In python 3, range() will become an iterator anyway and will be the preferred spelling (I'm not sure if xrange will still exist for compatability - probably not though). Using range() may make your code more portable going forward.

• range() can actually be faster in some cases - eg. if iterating over the same sequence multiple times. xrange has to reconstruct the integer object every time, but range will have real integer objects. (It will always perform worse in terms of memory however)

• xrange isn't usable in all cases where a real list is needed. For instance, it doesn't support slices, or any list methods.

[Edit] There are a couple of posts mentioning how range() will be upgraded by the 2to3 tool. For the record, here's the output of running the tool on some sample usages of range() and xrange()

RefactoringTool: Skipping implicit fixer: buffer
RefactoringTool: Skipping implicit fixer: idioms
RefactoringTool: Skipping implicit fixer: ws_comma
--- range_test.py (original)
+++ range_test.py (refactored)
@@ -1,7 +1,7 @@

 for x in range(20):
-    a=range(20)
+    a=list(range(20))
     b=list(range(20))
     c=[x for x in range(20)]
     d=(x for x in range(20))
-    e=xrange(20)
+    e=range(20)

As you can see, when used in a for loop or comprehension, or where already wrapped with list(), range is left unchanged.

Answer 5

range() returns a list, xrange() returns an xrange object.

xrange() is a bit faster, and a bit more memory efficient. But the gain is not very large.

The extra memory used by a list is of course not just wasted, lists have more functionality (slice, repeat, insert, ...). Exact differences can be found in the documentation. There is no bonehard rule, use what is needed.

Python 3.0 is still in development, but IIRC range() will very similar to xrange() of 2.X and list(range()) can be used to generate lists.

Answer 6

Okay, everyone here as a different opinion as to the tradeoffs and advantages of xrange versus range. They're mostly correct, xrange is an iterator, and range fleshes out and creates an actual list. For the majority of cases, you won't really notice a difference between the two. (You can use map with range but not with xrange, but it uses up more memory.)

What I think you rally want to hear, however, is that the preferred choice is xrange. Since range in Python 3 is an iterator, the code conversion tool 2to3 will correctly convert all uses of xrange to range, and will throw out an error or warning for uses of range. If you want to be sure to easily convert your code in the future, you'll use xrange only, and list(xrange) when you're sure that you want a list. I learned this during the CPython sprint at PyCon this year (2008) in Chicago.

Answer 7

No, they both have their uses:

Use xrange() when iterating, as it saves memory. Say:

for x in xrange(1, one_zillion):

rather than:

for x in range(1, one_zillion):

On the other hand, use range() if you actually want a list of numbers.

multiples_of_seven = range(7,100,7)
print "Multiples of seven < 100: ", multiples_of_seven