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Question

How can I add non-sequential numbers to a range?

Answer 1

+14 A:

Use the built-in + operator to append your non-sequential numbers to the range.

for x in range(750, 765) + [769, 770, 774]: print x

jcoon 2009-03-24 17:31:23

-1. This is not a good answer, nor is it for any others. itertools.chain() should be used.

Devin Jeanpierre 2009-03-24 17:37:14

for adding 3 numbers? that's hardly a performance hit. It will require more time to import itertools.If this is being done in a loop over thousands of ranges, then yes, maybe you should consider the chain method.

jcoon 2009-03-24 17:45:37

+1: Simple list concatenation.

S.Lott 2009-03-24 17:47:27

The range builtin uses a generator and will not allocate all the numbers in memory unless necessary. By doing the concatenation your forcing it to be allocated.

mustpax 2009-03-24 17:58:49

@multipax: No, it always creates a list in 2.x . In 3.0 it returns a non-list iterable, but it won't work like that.

Devin Jeanpierre 2009-03-24 18:22:35

It's not just three numbers. This actually creates 15 numbers in memory, 3 numbers in memory, then copies the 15 and 3 into a new 18-sized block in memory. It's just not decent, and won't work well for larger numbers. And there's no cost to using itertools.chain(), so why do otherwise at all?

Devin Jeanpierre 2009-03-24 18:23:23

+1 for being clear and concise and simply solving the stated problem

David Zaslavsky 2009-03-24 18:37:24

Premature optimization is premature.

Robert Rossney 2009-03-24 20:12:14

Yes it is, but it's not harmful. Is there any downside to premature optimization when it boils down to using the same amount of effort, sacrificing no flexibility, and in fact actually gaining flexibility (noticed how people had to use list(range()) for 3.0?)? Dogmatic avoidance means little.

Devin Jeanpierre 2009-03-24 20:23:52

Answer 2

+1 A:

are you looking for this:

mylist = range(750, 765)
mylist.extend([769, 770, 774])

Vasil 2009-03-24 17:32:18

I thought about doing it this way, but I knew there had to be a better, more concise way. Good suggestion though.

adam 2009-03-24 17:37:16

yes, the accepted answer is shorter. I thought you needed to store the list for later use.

Vasil 2009-03-24 17:42:27

You are right, I do need to store it. List comprehension to the rescue! mylist = [x for x in range(750, 765) + [769, 770, 774]]

adam 2009-03-24 17:47:31

@adam: The comprehension is actually redundant there. "mylist = range(750,765)+[769,770,774]" gives the same result without a needless extra iteration. In python3 it doesn't as range() isn't a list, but you can do the same with "mylist = list(range(750,765) + [769,770,774]" instead.

Brian 2009-03-24 17:58:24

Good call Brian, I'm glad I brought that up.

adam 2009-03-24 18:36:26

Answer 3

+10 A:

There are two ways to do it.

>>> for x in range(5, 7) + [8, 9]: print x
...
5
6
8
9
>>> import itertools
>>> for x in itertools.chain(xrange(5, 7), [8, 9]): print x
...
5
6
8
9

itertools.chain() is by far superior, since it allows you to use arbitrary iterables, rather than just lists and lists. It's also more efficient, not requiring list copying. And it lets you use xrange, which you should when looping.

Devin Jeanpierre 2009-03-24 17:33:50

I am not familiar with the itertools library. Thank you for suggesting it. I'll read up on it.

adam 2009-03-24 17:39:45

Answer 4

+4 A:

The other answers on this page will serve you well. Just a quick note that in Python3.0, range is an iterator (like xrange was in Python2.x... xrange is gone in 3.0). If you try to do this in Python 3.0, be sure to create a list from the range iterator before doing the addition:

for x in list(range(750, 765)) + [769, 770, 774]: print(x)

Jarret Hardie 2009-03-24 17:34:51

yeah, and be sure to use brackets with functions!

SilentGhost 2009-03-24 20:00:11

Ah, thank you. You have no idea how many times I've gotten a syntax error in Python 3.0 because of the darn print function!

Jarret Hardie 2009-03-24 20:21:35

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How can I add non-sequential numbers to a range?

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