Append a value to a list and move all values over

if i st开发者_StackOverflow社区art off with :

a=[1,2,4]

and i want the result to be

a=[1,3,2,4]

how do i do this append?

In [18]: a=[1,2,4]

In [19]: a[1:1]=[3]

In [20]: a
Out[20]: [1, 3, 2, 4]

or

In [22]: a.insert(1,3)

In [24]: a
Out[24]: [1, 3, 2, 4]

With the first (slice) notation, you can even insert multiple elements (similar to extend, but not necessarily at the end of the list):

In [26]: a[1:1]=[3,5]

In [27]: a
Out[27]: [1, 3, 5, 2, 4]

whereas with the insert method, you can only insert one element:

In [30]: a.insert(1,[3,5])

In [31]: a
Out[31]: [1, [3, 5], 2, 4]

The slice notation can also be used to modify or remove parts of a list.

a.insert( 1, 3 )

You can do this with the slice operator:

a[1:1] = (3,)

Or with the insert function:

a.insert(1, 3)

In both cases, position 1 refers to the second slot in the list.