Why is there no xrange function in Python3

Question

Recently I started using Python3 and it s lack of xrange hurts   Simple example   1  Python2   from time import time as t def count      st   t      x for x in xrange 10000000  if x 4    0    et   t     print et-st count     2  Python3   from time import time as t  def xrange x        return iter range x    def count        st   t        x for x in xrange 10000000  if x 4    0      et   t       print  et-st  count     The results are  respectively   1  1 53888392448 2  3 215819835662842  Why is that  I mean  why xrange s been removed  It s such a great tool to learn  For the beginners  just like myself  like we all were at some point  Why remove it  Can somebody point me to the proper PEP  I can t find it   Cheers

User · Answer

xrange from Python 2 is a generator and implements iterator while range is just a function  In Python3 I don t know why was dropped off the xrange

User · Answer

Python 3 s range type works just like Python 2 s xrange  I m not sure why you re seeing a slowdown  since the iterator returned by your xrange function is exactly what you d get if you iterated over range directly   I m not able to reproduce the slowdown on my system  Here s how I tested   Python 2  with xrange   Python 2 7 3  default  Apr 10 2012  23 24 47   MSC v 1500 64 bit  AMD64   on win32 Type  copyright    credits  or  license    for more information   gt  gt  gt  import timeit  gt  gt  gt  timeit timeit   x for x in xrange 1000000  if x 4   number 100  18 631936646865853   Python 3  with range is a tiny bit faster   Python 3 3 0  v3 3 0 bd8afb90ebf2  Sep 29 2012  10 57 17   MSC v 1600 64 bit  AMD64   on win32 Type  copyright    credits  or  license    for more information   gt  gt  gt  import timeit  gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 100  17 31399508687869   I recently learned that Python 3 s range type has some other neat features  such as support for slicing  range 10 100 2  5 25 5  is range 20  60  10

User · Answer

comp    python  Python 2 7 6  default  Jun 22 2015  17 58 13    GCC 4 8 2  on linux2   gt  gt  gt  import timeit  gt  gt  gt  timeit timeit   x for x in xrange 1000000  if x 4   number 100    5 656799077987671   gt  gt  gt  timeit timeit   x for x in xrange 1000000  if x 4   number 100    5 579368829727173   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 100    21 54827117919922   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 100    22 014557123184204  With timeit number 1 param    gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 1    0 2245171070098877   gt  gt  gt  timeit timeit   x for x in xrange 1000000  if x 4   number 1    0 10750913619995117  comp    python3 Python 3 4 3  default  Oct 14 2015  20 28 29    GCC 4 8 4  on linux   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 100    9 113872020003328   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 100    9 07014398300089  With timeit number 1 2 3 4 param works quick and in linear way    gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 1    0 09329321900440846   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 2    0 18501482300052885   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 3    0 2703447980020428   gt  gt  gt  timeit timeit   x for x in range 1000000  if x 4   number 4    0 36209142999723554  So it seems if we measure 1 running loop cycle like timeit timeit   x for x in range 1000000  if x 4   number 1   as we actually use in real code  python3 works quick enough  but in repeated loops python 2 xrange   wins in speed against range   from python 3

User · Answer

One way to fix up your python2 code is   import sys  if sys version info  gt    3  0       def xrange  args    kwargs           return iter range  args    kwargs

User · Answer

Some performance measurements  using timeit instead of trying to do it manually with time   First  Apple 2 7 2 64-bit   In  37    timeit collections deque  x for x in xrange 10000000  if x 4    0   maxlen 0  1 loops  best of 3  1 05 s per loop   Now  python org 3 3 0 64-bit   In  83    timeit collections deque  x for x in range 10000000  if x 4    0   maxlen 0  1 loops  best of 3  1 32 s per loop  In  84    timeit collections deque  x for x in xrange 10000000  if x 4    0   maxlen 0  1 loops  best of 3  1 31 s per loop  In  85    timeit collections deque  x for x in iter range 10000000   if x 4    0   maxlen 0   1 loops  best of 3  1 33 s per loop   Apparently  3 x range really is a bit slower than 2 x xrange  And the OP s xrange function has nothing to do with it   Not surprising  as a one-time call to the   iter   slot isn t likely to be visible among 10000000 calls to whatever happens in the loop  but someone brought it up as a possibility    But it s only 30  slower  How did the OP get 2x as slow  Well  if I repeat the same tests with 32-bit Python  I get 1 58 vs  3 12  So my guess is that this is yet another of those cases where 3 x has been optimized for 64-bit performance in ways that hurt 32-bit   But does it really matter  Check this out  with 3 3 0 64-bit again   In  86    timeit  x for x in range 10000000  if x 4    0  1 loops  best of 3  3 65 s per loop   So  building the list takes more than twice as long than the entire iteration    And as for  consumes much more resources than Python 2 6    from my tests  it looks like a 3 x range is exactly the same size as a 2 x xrange   and  even if it were 10x as big  building the unnecessary list is still about 10000000x more of a problem than anything the range iteration could possibly do   And what about an explicit for loop instead of the C loop inside deque   In  87   def consume x                for i in x                   pass In  88    timeit consume x for x in range 10000000  if x 4    0  1 loops  best of 3  1 85 s per loop   So  almost as much time wasted in the for statement as in the actual work of iterating the range   If you re worried about optimizing the iteration of a range object  you re probably looking in the wrong place     Meanwhile  you keep asking why xrange was removed  no matter how many times people tell you the same thing  but I ll repeat it again  It was not removed  it was renamed to range  and the 2 x range is what was removed   Here s some proof that the 3 3 range object is a direct descendant of the 2 x xrange object  and not of the 2 x range function   the source to 3 3 range and 2 7 xrange  You can even see the change history  linked to  I believe  the change that replaced the last instance of the string  xrange  anywhere in the file    So  why is it slower   Well  for one  they ve added a lot of new features  For another  they ve done all kinds of changes all over the place  especially inside iteration  that have minor side effects  And there d been a lot of work to dramatically optimize various important cases  even if it sometimes slightly pessimizes less important cases  Add this all up  and I m not surprised that iterating a range as fast as possible is now a bit slower  It s one of those less-important cases that nobody would ever care enough to focus on  No one is likely to ever have a real-life use case where this performance difference is the hotspot in their code

User · Answer

Python3 s range is Python2 s xrange  There s no need to wrap an iter around it  To get an actual list in Python3  you need to use list range        If you want something that works with Python2 and Python3  try this  try      xrange except NameError      xrange   range

[python] Why is there no xrange function in Python3?

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