Insert item before each element of a list

[Peter Otten]

mooremathewl at gmail.com wrote:

> What's the best way to accomplish this?  Am I over-complicating it?  My
> gut feeling is there is a better way than the following:
> 
>>>> import itertools
>>>> x = [1, 2, 3]
>>>> y = list(itertools.chain.from_iterable(('insertme', x[i]) for i in
>>>> range(len(x)))) y
> ['insertme', 1, 'insertme', 2, 'insertme', 3]

Less general than chain.from_iterable(izip(repeat("insertme"), x)):

>>> x = [1, 2, 3]
>>> y = 2*len(x)*["insertme"]
>>> y[1::2] = x
>>> y
['insertme', 1, 'insertme', 2, 'insertme', 3]