Extend: merge strings on a list from other lists (or variables) at the same time

Question

I have 3 different lists and I need to merge them. It is easy when you need to extend a list with just an element or adding an inteire list. But with more lists or adding a variable in the middle, it seems impossible.

list1 = [ 'a', 'b', 'c']
list2 = [ 'd', 'e', 'f']
list3 = ['g', 'h', 'i']

Adding just one list:

list1.extend(list3)

Return:

['a', 'b', 'c', 'g', 'h', 'i']

Adding two lists:

list1.extend((list2,list3))

Return two lists inside another list:

['a', 'b', 'c', ['d', 'e', 'f'], ['g', 'h', 'i']]

Adding two list with operator '+':

list1.extend((list2 + list3))

Returns

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

but if you need to do something like:

list1.extend(('test' + list2 + fetch[0] + list3 + etc, etc, etc))

will not works.Can't concatenate.

A temporary solution adding a loop could be:

for l1 in list2:
    list1.extend(l1)
for l2 in list3:
    list1.extend(l2)

to finally have:

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

Clearly a waste of lines and cycles

Is there a more efficient way to archive that without using external modules?

EDIT: the example of simple lists is just to understand what basically I need. The real problem is adding string or number or index on a single line of '.extend'.

SOLVED:

Wayne Werner drive me to the right direction to concatenate different type of elements.

list1 = [ 'a', 'b', 'c']
list2 = [ 'd', 'e', 'f']
list3 = ['g', 'h', 'i']

for other_list in (['test'], str(1), list2[2], list2[1]):
    list1.extend(other_list)

Result:

['a', 'b', 'c', 'test', '1', 'f', 'e']

Is your expected output equivalent to `list1 + list2 + list3`?? — Two-Bit Alchemist, Jun 08 '16 at 19:05
@Two-BitAlchemist: no. I realized (after) that the example is not what I was looking for. I've updated my question.Next time I'll ready again before sending out. I have some trouble when I need to add different type of elements on a list. — Federico Leoni, Jun 08 '16 at 21:46
This will not work with strings having more than one character since they are also iterable. You will have to use an `isinstance` test to decide whether to extend or append — Two-Bit Alchemist, Jun 09 '16 at 12:15

score 2 · Answer 1 · answered Jun 08 '16 at 19:05

2

Just use extend for each of the lists you want to add on:

list1.extend(list2)
list1.extend(list3)

answered Jun 08 '16 at 19:05

Scott Hunter

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score 2 · Accepted Answer · answered Jun 08 '16 at 19:50

2

If you're looking for a clean way of extending a single list with N number of other lists, it's as simple as that:

my_list = ['a', 'b', 'c']
for other_list in (some_iterable, some_other_iterable, another_iterable):
    my_list.extend(other_list)

I can't think of any more reasonable solution than that.

answered Jun 08 '16 at 19:50

Wayne Werner

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Yes, for now is the best solution possible. Thanks. – Federico Leoni Jun 08 '16 at 21:03

score 1 · Answer 3 · answered Jun 08 '16 at 19:47

1

You can extend one of the lists with the addition of the other two:

list1 = [ 'a', 'b', 'c']
list2 = [ 'd', 'e', 'f']
list3 = ['g', 'h', 'i']

list3.extend(lis1 + list2)

answered Jun 08 '16 at 19:47

Moses Koledoye

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It's a step forward, but if you try something like list1.extend(list2[1]+list3) it doesn't works. – Federico Leoni Jun 08 '16 at 20:47
If you change a solution that works, why would you expect it to still work? – Scott Hunter Jun 08 '16 at 20:48
@ScottHunter I was also going to say that – Moses Koledoye Jun 08 '16 at 20:49
I do apologize, I've edited my question because it was not clear of what I need. – Federico Leoni Jun 08 '16 at 21:37

Extend: merge strings on a list from other lists (or variables) at the same time

3 Answers3