Python 2: insert existing list inside of new explicit list definition

Question

This may not be possible, but if it is, it'd be convenient for some code I'm writing:

ListOne = ['jumps', 'over', 'the']
ListTwo = ['The', 'quick', 'brown', 'fox', ListOne, 'lazy', 'dog!']

If I do this, I'll end up with ListOne being a single item being a list inside of ListTwo.

But instead, I want to expand ListOne into ListTwo, but I don't want to have to do something like:

ListOne = ['jumps', 'over', 'the']
ListTwo = ['The', 'quick', 'brown', 'fox']
ListTwo.extend(ListOne)
ListTwo.extend(['lazy', 'dog!']

This will work but it's not as readable as the above code.

Is this possible?

What you want to do is to flatten the list. That's been covered here: http://stackoverflow.com/questions/952914/making-a-flat-list-out-of-list-of-lists-in-python and http://stackoverflow.com/questions/406121/flattening-a-shallow-list-in-python and http://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists-in-python and http://stackoverflow.com/questions/5409224/python-recursively-flatten-a-list — Sunita Venkatachalam, Jul 16 '13 at 07:34

grc · Accepted Answer · 2013-07-16T07:32:12.907

8

You can just use the + operator to concatenate lists:

ListOne = ['jumps', 'over', 'the']
ListTwo = ['The', 'quick', 'brown', 'fox'] + ListOne + ['lazy', 'dog!']

ListTwo will be:

['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog!']

edited Jul 16 '13 at 07:32

answered Jul 16 '13 at 07:26

grc

22,885
5
42
63

Turned out to be the simplest way to get it to work. Thanks, I always forget about list concatenation. – fdmillion Jul 22 '13 at 02:23

score 2 · Answer 2 · answered Jul 16 '13 at 07:27

2

Another alternative is to use slicing assignment:

>>> ListOne = ['jumps', 'over', 'the']
>>> ListTwo = ['The', 'quick', 'brown', 'fox', 'lazy', 'dog!']
>>> ListTwo[4:4] = ListOne
>>> ListTwo
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog!']

answered Jul 16 '13 at 07:27

Inbar Rose

41,843
24
85
131

1

This avoids the temporary list that @grc's answer creates – John La Rooy Jul 16 '13 at 07:29

score 1 · Answer 3 · answered Jul 16 '13 at 07:31

1

>>> ListOne = ['jumps', 'over', 'the']
>>> from itertools import chain
>>> [x for x in chain(['The', 'quick', 'brown', 'fox'], ListOne, ['lazy', 'dog!'])]
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog!']

answered Jul 16 '13 at 07:31

John La Rooy

295,403
53
369
502

score 0 · Answer 4 · edited Jul 16 '13 at 07:41

0

Why not concatenate?

>>> ListTwo = ['The', 'quick', 'brown', 'fox']
>>> ListOne = ['jumps', 'over', 'the']
>>> ListTwo + ListOne
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the']
>>> ListTwo + ListOne + ['lazy', 'dog!']
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog!']

edited Jul 16 '13 at 07:41

Inbar Rose

41,843
24
85
131

answered Jul 16 '13 at 07:38

aayoubi

11,285
3
22
20

Python 2: insert existing list inside of new explicit list definition

4 Answers4