How can I enable xrange in Python 3 for portability?

Question

I wrote a script which I wanted to enable for both Python 2 and Python 3.

After importing division and print_function from __future__, my only concern was that my range returns a whole array in Python 2, wasting time and memory.

I added the following 3 lines at the beginning of the script, as a workaround:

if sys.version_info[0] == 3:
    def xrange(i):
        return range(i)

Then, I only used xrange in my code.

Is there some more elegant way to do it rather than my workaround?

There are dedicated libraries to it for you, e.g. [`six`](https://pypi.python.org/pypi/six). — Łukasz Rogalski, Jun 15 '16 at 11:39
Is your script really so time- and memory-intensive that it matters? — Bryan Oakley, Jun 15 '16 at 11:50
I usually write the code for Python 3 (`dict.items()`, `range()`, ...) and accept that it may perform sub-optimally with Python 2. So far no-one ever complained because most of the time the memory overhead is negligible. — Georg Schölly, Aug 17 '18 at 12:51

score 13 · Accepted Answer · answered Jun 15 '16 at 11:49

13

You can simplify it a bit:

if sys.version_info[0] == 3:
    xrange = range

I would do it the other way around:

if sys.version_info[0] == 2:
    range = xrange

If you ever want to drop Python 2.x support, you can just remove those two lines without going through all your code.

However, I strongly suggest considering the six library. It is the de-facto standard for enabling Python 2 and 3 compatibility.

from six.moves import range

answered Jun 15 '16 at 11:49

Daniel Hepper

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I totally agree that the other way you suggest seems more usable. It's actually making Python2's `range` act like Python3's `range`, instead of intoducing `xrange` to Python3 and leaving Python3's `range` different from Python2's `range` – SomethingSomething Aug 17 '17 at 07:52
in python3 the second version gives an error, as there is an "if" statement which is not executed, but then `range` variable is considered undefined. This is frustrating. I switched to `six` but it would be actually more preferable to avoid using an additional package. – Sergey Dovgal May 31 '18 at 11:37
@SergeyDovgal I just verified that the second version works as expected in Python 3.6.3. Or do you mean that you get an error in your IDE? – Daniel Hepper Jun 04 '18 at 12:36
@DanielHepper You are right, I just tried it in an interpreter and it works. However, I recall that the error obtained was related to code launched after installation script. Essentially I got "UnboundLocalError: local variable referenced before assignment", but I need to explain how to reproduce it. I will recall and describe a bit after. – Sergey Dovgal Jun 04 '18 at 16:15

How can I enable xrange in Python 3 for portability?

1 Answers1