What is the syntax to insert one list into another list in python?

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Question :

What is the syntax to insert one list into another list in python?

Given two lists:

x = [1,2,3]
y = [4,5,6]

What is the syntax to:

  1. Insert x into y such that y now looks like [1, 2, 3, [4, 5, 6]]?
  2. Insert all the items of x into y such that y now looks like [1, 2, 3, 4, 5, 6]?
Asked By: Soumya

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Answer #1:

Do you mean append?

>>> x = [1,2,3]
>>> y = [4,5,6]
>>> x.append(y)
>>> x
[1, 2, 3, [4, 5, 6]]

Or merge?

>>> x = [1,2,3]
>>> y = [4,5,6]
>>> x + y
[1, 2, 3, 4, 5, 6]
>>> x.extend(y)
>>> x
[1, 2, 3, 4, 5, 6] 
Answered By: Paolo Bergantino

Answer #2:

The question does not make clear what exactly you want to achieve.

List has the append method, which appends its argument to the list:

>>> list_one = [1,2,3]
>>> list_two = [4,5,6]
>>> list_one.append(list_two)
>>> list_one
[1, 2, 3, [4, 5, 6]]

There’s also the extend method, which appends items from the list you pass as an argument:

>>> list_one = [1,2,3]
>>> list_two = [4,5,6]
>>> list_one.extend(list_two)
>>> list_one
[1, 2, 3, 4, 5, 6]

And of course, there’s the insert method which acts similarly to append but allows you to specify the insertion point:

>>> list_one.insert(2, list_two)
>>> list_one
[1, 2, [4, 5, 6], 3, 4, 5, 6]

To extend a list at a specific insertion point you can use list slicing (thanks, @florisla):

>>> l = [1, 2, 3, 4, 5]
>>> l[2:2] = ['a', 'b', 'c']
>>> l
[1, 2, 'a', 'b', 'c', 3, 4, 5]

List slicing is quite flexible as it allows to replace a range of entries in a list with a range of entries from another list:

>>> l = [1, 2, 3, 4, 5]
>>> l[2:4] = ['a', 'b', 'c'][1:3]
>>> l
[1, 2, 'b', 'c', 5]
Answered By: Sergey

Answer #3:

foo = [1, 2, 3]
bar = [4, 5, 6]

foo.append(bar) --> [1, 2, 3, [4, 5, 6]]
foo.extend(bar) --> [1, 2, 3, 4, 5, 6]

http://docs.python.org/tutorial/datastructures.html

Answered By: Coding District

Answer #4:

You can also just do…

x += y
Answered By: user3707850

Answer #5:

If you want to add the elements in a list (list2) to the end of other list (list), then you can use the list extend method

list = [1, 2, 3]
list2 = [4, 5, 6]
list.extend(list2)
print list
[1, 2, 3, 4, 5, 6]

Or if you want to concatenate two list then you can use + sign

list3 = list + list2
print list3
[1, 2, 3, 4, 5, 6]
Answered By: squal

Answer #6:

If we just do x.append(y), y gets referenced into x such that any changes made to y will affect appended x as well. So if we need to insert only elements, we should do following:

x = [1,2,3]
y = [4,5,6]
x.append(y[:])

Answered By: Raj Stha

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