Merging an existing list into the middle of a Python list literal

Question

When declaring a list literal in Python, is it possible to merge an existing list into the declaration? For example:

l = [1, 2, 3]
n = [10, 20, 30, l, 50, 60, 70]

This results in the following:

[10, 20, 30, [1, 2, 3], 50, 60, 70]

Note that the list l itself has been added as a single element, but what I really want is for l's elements to be added individually to the target list, like this:

[10, 20, 30, 1, 2, 3, 50, 60, 70]

Amr Bekhit · Accepted Answer · 2017-10-24T09:18:32.263

1

As of Python 3.5 (See https://www.python.org/downloads/release/python-350/, PEP448), This can be done using Python's unpack operator, which is an asterisk before the list:

l = [1, 2, 3]
n = [10, 20, 30, *l, 50, 60, 70]

The result is:

[10, 20, 30, 1, 2, 3, 50, 60, 70]

edited Oct 24 '17 at 09:18

answered Oct 24 '17 at 09:09

Amr Bekhit

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@GPhilo Thanks for the heads up. Do you know when this was introduced into python 3? – Amr Bekhit Oct 24 '17 at 09:17
Found it - it was introduced in Python 3.5 – Amr Bekhit Oct 24 '17 at 09:19
1

AFAIR it was introduced in [PEP 448](https://www.python.org/dev/peps/pep-0448/) and Python 3.5 – GPhilo Oct 24 '17 at 09:19
For python2.7 use this solution, https://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists – Rahul K P Oct 24 '17 at 09:20

score 0 · Answer 2 · answered Oct 24 '17 at 09:50

0

This will works with l on any place

from itertools import chain   
for i in n:
   if isinstance(i, list):
      b+=list(chain(i))
   else:
      b+=[i]

answered Oct 24 '17 at 09:50

nick_gabpe

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Merging an existing list into the middle of a Python list literal

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